137-488: An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system . In higher organisms, the eye is a complex optical system that collects light from the surrounding environment, regulates its intensity through a diaphragm , focuses it through an adjustable assembly of lenses to form an image , converts this image into
274-605: A compound eye consisting of hundreds to thousands of ommatidia , that each produce a pixel of the entire image, the strepsipteran eyes consist of only a few dozen "eyelets" that each produce a complete image. These eyelets are separated by cuticle and/or setae, giving the cluster eye as a whole a blackberry-like appearance. The females of Stylopidia, which includes 97% of all described strepsipteran species and all modern strepsipteran families except Mengenillidae and Bahiaxenidae , are not known to leave their hosts and are neotenic in form, lacking wings, legs, and eyes, but have
411-455: A fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil . This occurs because the ommatidia which one observes "head-on" (along their optical axes ) absorb
548-465: A central point. An example would be when we use parentheses in writing. We tend to perceive all of the words in the parentheses as one section instead of individual words within the parentheses. The Law of Continuity tells us that objects are grouped together by their elements and then perceived as a whole. This usually happens when we see overlapping objects. We will see the overlapping objects with no interruptions. The Law of Past Experience refers to
685-457: A central point. The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out. Many small organisms such as rotifers , copepods and flatworms use such organs, but these are too small to produce usable images. Some larger organisms, such as scallops , also use reflector eyes. The scallop Pecten has up to 100 millimetre-scale reflector eyes fringing
822-428: A cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye. The body of Ophiocoma wendtii , a type of brittle star , is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons . The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect
959-426: A factor of 1,000 or more. Ocelli , some of the simplest eyes, are found in animals such as some of the snails . They have photosensitive cells but no lens or other means of projecting an image onto those cells. They can distinguish between light and dark but no more, enabling them to avoid direct sunlight . In organisms dwelling near deep-sea vents , compound eyes are adapted to see the infra-red light produced by
1096-640: A few facets, each with a retina capable of creating an image. With each eye producing a different image, a fused, high-resolution image is produced in the brain. The mantis shrimp has the world's most complex colour vision system. It has detailed hyperspectral colour vision. Trilobites , now extinct, had unique compound eyes. Clear calcite crystals formed the lenses of their eyes. They differ in this from most other arthropods, which have soft eyes. The number of lenses in such an eye varied widely; some trilobites had only one while others had thousands of lenses per eye. In contrast to compound eyes, simple eyes have
1233-404: A focusing lens , and often an iris . Muscles around the iris change the size of the pupil , regulating the amount of light that enters the eye and reducing aberrations when there is enough light. The eyes of most cephalopods , fish , amphibians and snakes have fixed lens shapes, and focusing is achieved by telescoping the lens in a similar manner to that of a camera . The compound eyes of
1370-403: A group, but we can also perceive three groups of two lines with seven objects in each line. The Law of Closure is the idea that we as humans still see a full picture even if there are gaps within that picture. There could be gaps or parts missing from a section of a shape, but we would still perceive the shape as whole. The Law of Symmetry refers to a person's preference to see symmetry around
1507-609: A high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina. This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration . Such a non-homogeneous lens is necessary for the focal length to drop from about 4 times the lens radius, to 2.5 radii. So-called under-focused lens eyes, found in gastropods and polychaete worms, have eyes that are intermediate between lens-less cup eyes and real camera eyes. Also box jellyfish have eyes with
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#17327656344371644-485: A human), close your eyes (preferably in a dark room) and press gently on the outside corner of one eye through the eyelid. You will see a visual spot toward the inside of your visual field, near your nose.) All stimuli received by the receptors are transduced to an action potential , which is carried along one or more afferent neurons towards a specific area ( cortex ) of the brain . Just as different nerves are dedicated to sensory and motors tasks, different areas of
1781-508: A large number of stylopidians targeting wasps and bees, while the largest family of strepsipterans, the Stylopidae , with over 27% of all described strepsipterans, targets bees exclusively. Very rarely, multiple females may live within a single stylopized host; multiple males within a single host are somewhat more common. Strepsiptera of the family Myrmecolacidae can influence their host's behaviour , causing their ant hosts to linger on
1918-403: A lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium . The second type is named the superposition eye. The superposition eye is divided into three types: The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to
2055-446: A limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays ). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 metres (36 ft) in radius. Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form
2192-586: A materialistic view of the mind. Some examples of human absolute thresholds for the nine to 21 external senses . Humans respond more strongly to multimodal stimuli compared to the sum of each single modality together, an effect called the superadditive effect of multisensory integration . Neurons that respond to both visual and auditory stimuli have been identified in the superior temporal sulcus . Additionally, multimodal "what" and "where" pathways have been proposed for auditory and tactile stimuli. External receptors that respond to stimuli from outside
2329-495: A mechanoreceptor. Photoreceptors convert light (visible electromagnetic radiation ) into signals. Chemical stimuli can be interpreted by a chemoreceptor that interprets chemical stimuli, such as an object's taste or smell, while osmoreceptors respond to a chemical solute concentrations of body fluids. Nociception (pain) interprets the presence of tissue damage, from sensory information from mechano-, chemo-, and thermoreceptors. Another physical stimulus that has its own type of receptor
2466-449: A parabolic mirror to focus the image; it combines features of superposition and apposition eyes. Another kind of compound eye, found in males of Order Strepsiptera , employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is similar to the 'schizochroal' compound eyes of some trilobites . Because each eyelet
2603-468: A particular color . Visible light is electromagnetic radiation with a wavelength between 380 and 720 nm. Wavelengths of electromagnetic radiation longer than 720 nm fall into the infrared range, whereas wavelengths shorter than 380 nm fall into the ultraviolet range. Light with a wavelength of 380 nm is blue whereas light with a wavelength of 720 nm is dark red . All other colors fall between red and blue at various points along
2740-418: A pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eyes". They are small, comprising up to about 100 cells covering about 100 μm. The directionality can be improved by reducing the size of the aperture, by incorporating
2877-497: A reflective layer behind the receptor cells, or by filling the pit with a refractile material. Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates (see infrared sensing in snakes ). However, pit organs are fitted with receptors rather different from photoreceptors, namely a specific transient receptor potential channel (TRP channels) called TRPV1 . The main difference
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#17327656344373014-464: A refractive cornea: these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution. In the eyes of most mammals , birds , reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air. In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas,
3151-614: A resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes , so are better suited to dark-dwelling creatures. Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being ciliated (as in the vertebrates) or rhabdomeric . These two groups are not monophyletic; the Cnidaria also possess ciliated cells, and some gastropods and annelids possess both. Some organisms have photosensitive cells that do nothing but detect whether
3288-471: A respective visual system (sense of vision), auditory system (sense of hearing), somatosensory system (sense of touch), olfactory system (sense of smell), and gustatory system (sense of taste). Those systems, in turn, contribute to vision , hearing , touch , smell , and the ability to taste . Internal sensation, or interoception, detects stimuli from internal organs and tissues. Many internal sensory and perceptual systems exist in humans, including
3425-439: A sense, but it is generally regarded as a cognitive (that is, post-sensory) function of the visual cortex of the brain where patterns and objects in images are recognized and interpreted based on previously learned information. This is called visual memory . The inability to see is called blindness . Blindness may result from damage to the eyeball, especially to the retina, damage to the optic nerve that connects each eye to
3562-498: A series of tiny bones to hair-like fibers in the inner ear , which detect mechanical motion of the fibers within a range of about 20 to 20,000 hertz , with substantial variation between individuals. Hearing at high frequencies declines with an increase in age. Inability to hear is called deafness or hearing impairment. Sound can also be detected as vibrations conducted through the body. Lower frequencies that can be heard are detected this way. Some deaf people are able to determine
3699-450: A set of electrical signals, and transmits these signals to the brain through neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, classified into compound eyes and non-compound eyes. Compound eyes are made up of multiple small visual units, and are common on insects and crustaceans . Non-compound eyes have
3836-404: A sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain. Focusing the image would also cause the sun's image to be focused on a few receptors, with
3973-495: A single erect image. Compound eyes are common in arthropods, annelids and some bivalved molluscs. Compound eyes in arthropods grow at their margins by the addition of new ommatidia. Apposition eyes are the most common form of eyes and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum. Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus ,
4110-516: A single lens and focus light onto the retina to form a single image. This type of eye is common in mammals, including humans. The simplest eyes are pit eyes. They are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. Eyes enable several photo response functions that are independent of vision. In an organism that has more complex eyes, retinal photosensitive ganglion cells send signals along
4247-454: A single lens. Jumping spiders have one pair of large simple eyes with a narrow field of view , augmented by an array of smaller eyes for peripheral vision . Some insect larvae , like caterpillars , have a type of simple eye ( stemmata ) which usually provides only a rough image, but (as in sawfly larvae) can possess resolving powers of 4 degrees of arc, be polarization-sensitive, and capable of increasing its absolute sensitivity at night by
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4384-416: A sound or smell) for transduction , meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition , behavior and thought . In organisms, a sensory organ consists of a group of interrelated sensory cells that respond to a specific type of physical stimulus. Via cranial and spinal nerves (nerves of
4521-478: A specific type of stimulus. For example, the general sensation and perception of touch, which is known as somatosensation, can be separated into light pressure, deep pressure, vibration, itch, pain, temperature, or hair movement, while the general sensation and perception of taste can be separated into submodalities of sweet , salty , sour , bitter , spicy, and umami , all of which are based on different chemicals binding to sensory neurons . Sensory receptors are
4658-404: A spherical lens, cornea and retina, but the vision is blurry. Heterogeneous eyes have evolved at least nine times: four or more times in gastropods , once in the copepods , once in the annelids , once in the cephalopods , and once in the chitons , which have aragonite lenses. No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens
4795-662: A stimulus is constant and unchanging, perceptual sensory adaptation occurs. During that process, the subject becomes less sensitive to the stimulus. Biological auditory (hearing), vestibular and spatial, and visual systems (vision) appear to break down real-world complex stimuli into sine wave components, through the mathematical process called Fourier analysis. Many neurons have a strong preference for certain sine frequency components in contrast to others. The way that simpler sounds and images are encoded during sensation can provide insight into how perception of real-world objects happens. Perception occurs when nerves that lead from
4932-669: A stronger sense of smell than humans. Some animal species lack one or more human sensory system analogues and some have sensory systems that are not found in humans, while others process and interpret the same sensory information in very different ways. For example, some animals are able to detect electrical fields and magnetic fields , air moisture , or polarized light . Others sense and perceive through alternative systems such as echolocation . Recent theory suggests that plants and artificial agents such as robots may be able to detect and interpret environmental information in an analogous manner to animals. Sensory modality refers to
5069-415: A transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index , and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with
5206-527: A well sclerotised cephalothorax (fused head and thorax ). Adult female mengenillids are wingless but are free living and somewhat mobile with legs and small eyes. This is probably also true for the bahiaxenids, though this has not been observed. Newly hatched primary (first instar ) larvae are on average 230 micrometres ( 1 ⁄ 128 in) in length, smaller than many single-celled organisms. They are highly mobile with well developed stemmata , which are able to distinguish color. The underside of
5343-472: Is phylogenetically very old, with various theories of phylogenesis. The common origin ( monophyly ) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 650-600 million years ago, and the PAX6 gene is considered a key factor in this. The majority of
5480-399: Is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light. Because the individual lenses are so small, the effects of diffraction impose
5617-411: Is a molecule called propylthiouracil (PROP) that some humans experience as bitter, some as almost tasteless, while others experience it as somewhere between tasteless and bitter. There is a genetic basis for this difference between perception given the same sensory stimulus. This subjective difference in taste perception has implications for individuals' food preferences, and consequently, health. When
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5754-429: Is a perception resulting from activation of neural receptors , generally in the skin including hair follicles , but also in the tongue , throat , and mucosa . A variety of pressure receptors respond to variations in pressure (firm, brushing, sustained, etc.). The touch sense of itching caused by insect bites or allergies involves special itch-specific neurons in the skin and spinal cord. The loss or impairment of
5891-411: Is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels. Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies , have specialised zones of ommatidia organised into
6028-404: Is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes. The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into
6165-482: Is attached to the tympanic membrane and articulates with the incus. The incus, in turn, articulates with the stapes. The stapes is then attached to the inner ear , where the sound waves will be transduced into a neural signal. The middle ear is connected to the pharynx through the Eustachian tube , which helps equilibrate air pressure across the tympanic membrane. The tube is normally closed but will pop open when
6302-438: Is based on their location relative to the stimuli. An exteroceptor is a receptor that is located near a stimulus of the external environment, such as the somatosensory receptors that are located in the skin. An interoceptor is one that interprets stimuli from internal organs and tissues, such as the receptors that sense the increase in blood pressure in the aorta or carotid sinus . The cells that interpret information about
6439-489: Is concerned with the nature of perceptual experience and the status of perceptual data , in particular how they relate to beliefs about, or knowledge of, the world. Historical inquiries into the underlying mechanisms of sensation and perception have led early researchers to subscribe to various philosophical interpretations of perception and the mind , including panpsychism , dualism , and materialism . The majority of modern scientists who study sensation and perception take on
6576-431: Is dedicated to the auditory system . The main point is to understand why humans are able to use sound in thinking outside of actually saying it. Relating to auditory cognitive psychology is psychoacoustics . Psychoacoustics is more directed at people interested in music. Haptics , a word used to refer to both taction and kinesthesia, has many parallels with psychoacoustics. Most research around these two are focused on
6713-465: Is described by Steven's power law . Signal detection theory quantifies the experience of the subject to the presentation of a stimulus in the presence of noise . There is internal noise and there is external noise when it comes to signal detection. The internal noise originates from static in the nervous system. For example, an individual with closed eyes in a dark room still sees something—a blotchy pattern of grey with intermittent brighter flashes—this
6850-549: Is encoded or transduced. Multimodality integrates different senses into one unified perceptual experience. For example, information from one sense has the potential to influence how information from another is perceived. Sensation and perception are studied by a variety of related fields, most notably psychophysics , neurobiology , cognitive psychology , and cognitive science . Sensory organs are organs that sense and transduce stimuli. Humans have various sensory organs (i.e. eyes, ears, skin, nose, and mouth) that correspond to
6987-399: Is great enough for this stage to be quickly "outgrown". This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles. The ocelli of insects bear a simple lens, but their focal point usually lies behind the retina; consequently, those can not form
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#17327656344377124-457: Is in a deep narrow fissure of the cephalothorax near the birth canal). Sperm passes through the opening directly into the body in a process called traumatic insemination , which has independently evolved in some other insects like bed bugs . Strepsiptera eggs hatch inside the female, and the planidium larvae can move around freely within the female's haemocoel ; this behavior is unique to these insects. The offspring consume their mother from
7261-410: Is internal noise. External noise is the result of noise in the environment that can interfere with the detection of the stimulus of interest. Noise is only a problem if the magnitude of the noise is large enough to interfere with signal collection. The nervous system calculates a criterion, or an internal threshold, for the detection of a signal in the presence of noise. If a signal is judged to be above
7398-409: Is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water—penguins and seals, for example—lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea. A unique feature of most mammal eyes is the presence of eyelids which wipe
7535-472: Is not well known to non-specialists, and the nearest they have to a common name is stylops , in reference to the genus Stylops . The name of the order translates to "twisted wing", giving rise to other common names used for the order, twisted-wing insects and twisted-winged parasites . Adult males are rarely observed, although specimens may be lured using cages containing virgin females. Nocturnal specimens can also be collected at light traps. Males of
7672-425: Is often multimodal. Multimodality integrates different senses into one unified perceptual experience. Information from one sense has the potential to influence how information from another is perceived. Multimodal perception is qualitatively different from unimodal perception. There has been a growing body of evidence since the mid-1990s on the neural correlates of multimodal perception. The philosophy of perception
7809-594: Is seen into patterns or groups: Common Fate, Similarity, Proximity, Closure, Symmetry, Continuity, and Past Experience. The Law of Common fate says that objects are led along the smoothest path. People follow the trend of motion as the lines/dots flow. The Law of Similarity refers to the grouping of images or objects that are similar to each other in some aspect. This could be due to shade, colour, size, shape, or other qualities you could distinguish. The Law of Proximity states that our minds like to group based on how close objects are to each other. We may see 42 objects in
7946-428: Is temperature, which is sensed through a thermoreceptor that is either sensitive to temperatures above (heat) or below (cold) normal body temperature. Each sense organ (eyes or nose, for instance) requires a minimal amount of stimulation in order to detect a stimulus. This minimum amount of stimulus is called the absolute threshold. The absolute threshold is defined as the minimum amount of stimulation necessary for
8083-471: Is that photoreceptors are G-protein coupled receptors but TRP are ion channels . The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable. The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with
8220-523: Is the sensation of potentially damaging stimuli. Mechanical, chemical, or thermal stimuli beyond a set threshold will elicit painful sensations. Stressed or damaged tissues release chemicals that activate receptor proteins in the nociceptors. For example, the sensation of heat associated with spicy foods involves capsaicin , the active molecule in hot peppers. Low frequency vibrations are sensed by mechanoreceptors called Merkel cells , also known as type I cutaneous mechanoreceptors. Merkel cells are located in
8357-442: The arthropods are composed of many simple facets which, depending on anatomical detail, may give either a single pixelated image or multiple images per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors arranged hexagonally, which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera , have compound eyes of only
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#17327656344378494-489: The cell membrane that mediates a physiological change in a neuron, most often through the opening of ion channels or changes in the cell signaling processes. Transmembrane receptors are activated by chemicals called ligands . For example, a molecule in food can serve as a ligand for taste receptors. Other transmembrane proteins, which are not accurately called receptors, are sensitive to mechanical or thermal changes. Physical changes in these proteins increase ion flow across
8631-439: The copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia , has two lenses in each eye, arranged like those in a telescope. Such arrangements are rare and poorly understood, but represent an alternative construction. Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have
8768-407: The crown group , but are all more closely related to modern strepsiperans than Protoxenos is. The finding of a parasitic first instar in the same deposit indicates that the parasitic lifestyle of the group has likely existed nearly unchanged for 100 million years, though their evolutionary history prior to this remains a mystery. The idea that mengellinids' targeting of zygentomans represents
8905-565: The femur . The larvae are very active as they only have a limited amount of time to find a host before they exhaust their energy reserves. These first- instar larvae have stemmata (simple, single-lens eyes). When the larvae latch onto a host, they enter it by secreting enzymes that soften the cuticle, usually in the abdominal region of the host. Some species have been reported to enter the eggs of hosts. Larvae of Stichotrema dallatorreanurn Hofeneder from Papua New Guinea were found to enter their orthopteran host's tarsus (foot). Once inside
9042-419: The incident light , while those to one side reflect it. There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa . The shrimp has an eye of
9179-414: The retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex . Complex eyes distinguish shapes and colours . The visual fields of many organisms, especially predators, involve large areas of binocular vision for depth perception . In other organisms, particularly prey animals, eyes are located to maximise
9316-410: The sensory organs (e.g. eye) to the brain are stimulated, even if that stimulation is unrelated to the target signal of the sensory organ. For example, in the case of the eye, it does not matter whether light or something else stimulates the optic nerve, that stimulation will results in visual perception, even if there was no visual stimulus to begin with. (To prove this point to yourself (and if you are
9453-433: The stratum basale of the epidermis . Deep pressure and vibration is transduced by lamellated ( Pacinian ) corpuscles, which are receptors with encapsulated endings found deep in the dermis, or subcutaneous tissue. Light touch is transduced by the encapsulated endings known as tactile ( Meissner ) corpuscles. Follicles are also wrapped in a plexus of nerve endings known as the hair follicle plexus. These nerve endings detect
9590-594: The vestibular system (sense of balance) sensed by the inner ear and providing the perception of spatial orientation ; proprioception (body position); and nociception (pain). Further internal chemoreception - and osmoreception -based sensory systems lead to various perceptions, such as hunger , thirst , suffocation , and nausea , or different involuntary behaviors, such as vomiting . Nonhuman animals experience sensation and perception, with varying levels of similarity to and difference from humans and other animal species. For example, other mammals in general have
9727-416: The "blue" cones predominantly. The relative activation of the three different cones is calculated by the brain, which perceives the color as blue. However, cones cannot react to low-intensity light, and rods do not sense the color of light. Therefore, our low-light vision is—in essence—in grayscale . In other words, in a dark room, everything appears as a shade of gray . If you think that you can see colors in
9864-678: The Central and Peripheral nervous systems that relay sensory information to and from the brain and body), the different types of sensory receptor cells (such as mechanoreceptors , photoreceptors , chemoreceptors , thermoreceptors ) in sensory organs transduct sensory information from these organs towards the central nervous system, finally arriving at the sensory cortices in the brain , where sensory signals are processed and interpreted (perceived). Sensory systems, or senses, are often divided into external (exteroception) and internal ( interoception ) sensory systems. Human external senses are based on
10001-998: The Halictophagidae are found on leafhoppers, treehoppers, and mole cricket hosts. Strepsipteran insects in the genus Xenos parasitize Polistes carnifex , a species of social wasps. These obligate parasites infect the developing wasp larvae in the nest and are present within the abdomens of female wasps when they hatch out. Here they remain until they thrust through the cuticle and pupate (males) or release infective first- instar larvae onto flowers (females). These larvae are transported back to their nests by foraging wasps. After: † Protoxenidae † Cretostylopidae † Phthanoxenidae † Mengeidae Bahiaxenidae Mengenillidae Corioxenidae Bohartillidae Halictophagidae Elenchidae † Protelencholacidae Myrmecolacidae Callipharixenidae Xenidae Stylopidae Some insects which have been considered pests may have strepsipteran endoparasites. Inoculation of
10138-497: The Strepsiptera have wings , legs , eyes , and antennae , though their mouthparts cannot be used for feeding. Many have mouthparts modified into sensory structures. The males bear a superficial resemblance to flies. The forewings are modified into small club-shaped structures called halteres , which sense gyroscopic information. A similar organ exists in flies, though in that group the hindwings are modified instead, and
10275-618: The ability to feel anything touched is called tactile anesthesia . Paresthesia is a sensation of tingling, pricking, or numbness of the skin that may result from nerve damage and may be permanent or temporary. Two types of somatosensory signals that are transduced by free nerve endings are pain and temperature. These two modalities use thermoreceptors and nociceptors to transduce temperature and pain stimuli, respectively. Temperature receptors are stimulated when local temperatures differ from body temperature . Some thermoreceptors are sensitive to just cold and others to just heat. Nociception
10412-489: The advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race" among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as
10549-652: The ancestral ecology of the group as a whole has been considered questionable. The vast majority of living strepispterans are placed within the grouping Stylopidia, which includes the families Corioxenidae , Halictophagidae , Callipharixenidae , Bohartillidae , Elenchidae , Myrmecolacidae , Stylopidae , Protelencholacidae (extinct) and Xenidae . All Stylopidia have endoparasitic females having multiple genital openings. Two living families, Mengenillidae and Bahiaxenidae , are placed outside of this group, along with several extinct families. The Stylopidae have four-segmented tarsi and four- to six-segmented antennae, with
10686-404: The basis of the type of stimuli they transduce. The different types of functional receptor cell types are mechanoreceptors , photoreceptors , chemoreceptors ( osmoreceptor ), thermoreceptors , electroreceptors (in certain mammals and fish), and nociceptors . Physical stimuli, such as pressure and vibration, as well as the sensation of sound and body position (balance), are interpreted through
10823-415: The basis of three different criteria: cell type , position, and function. Receptors can be classified structurally on the basis of cell type and their position in relation to stimuli they sense. Receptors can further be classified functionally on the basis of the transduction of stimuli, or how the mechanical stimulus, light, or chemical changed the cell membrane potential . One way to classify receptors
10960-452: The body are called exteroceptors . Human external sensation is based on the sensory organs of the eyes , ears , skin , vestibular system , nose , and mouth , which contribute, respectively, to the sensory perceptions of vision , hearing , touch , balance , smell , and taste . Smell and taste are both responsible for identifying molecules and thus both are types of chemoreceptors . Both olfaction (smell) and gustation (taste) require
11097-407: The body is covered in minute hair-like structures (microtrichia), which allow the larvae to stick to wet surfaces via capillary action . At the back of the body are well developed large bristle-like cerci , which are attached to muscles, which allow the larvae to jump. The tarsal segment of their legs have structures which allow them to cling to their hosts. Later larval instars which develop inside
11234-546: The brain (cortices) are similarly dedicated to different sensory and perceptual tasks. More complex processing is accomplished across primary cortical regions that spread beyond the primary cortices. Every nerve, sensory or motor , has its own signal transmission speed. For example, nerves in the frog's legs have a 90 ft/s (99 km/h) signal transmission speed, while sensory nerves in humans, transmit sensory information at speeds between 165 ft/s (181 km/h) and 330 ft/s (362 km/h). Perceptual experience
11371-515: The brain, and/or from stroke ( infarcts in the brain). Temporary or permanent blindness can be caused by poisons or medications. People who are blind from degradation or damage to the visual cortex, but still have functional eyes, are actually capable of some level of vision and reaction to visual stimuli but not a conscious perception; this is known as blindsight . People with blindsight are usually not aware that they are reacting to visual sources, and instead just unconsciously adapt their behavior to
11508-432: The cells or structures that detect sensations. Stimuli in the environment activate specialized receptor cells in the peripheral nervous system . During transduction, physical stimulus is converted into action potential by receptors and transmitted towards the central nervous system for processing. Different types of stimuli are sensed by different types of receptor cells . Receptor cells can be classified into types on
11645-639: The clade Coleopterida . The most basal strepsipteran is the fossil Protoxenos janzeni discovered in Eocene aged Baltic amber , while the most basal living strepsipteran is Bahiaxenos relictus , the sole member of the family Bahiaxenidae . The earliest known strepsipteran fossils are those of Cretostylops engeli (Cretostylopdiae) and Kinzelbachilla ellenbergeri , Phthanoxenos nervosus and Heterobathmilla kakopoios (Phthanoxenidae), discovered in middle Cretaceous Burmese amber from Myanmar , around 99 million years old, which all lie outside
11782-464: The clade Mecopterida (containing the Diptera and Lepidoptera), but found no strong evidence for affinity with any other extant group. Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction . Most modern molecular studies find strepsipterans as the sister group of beetles (Coleoptera), with both groups together forming
11919-524: The criterion, thus the signal is differentiated from the noise, the signal is sensed and perceived. Errors in signal detection can potentially lead to false positives and false negatives . The sensory criterion might be shifted based on the importance of the detecting the signal. Shifting of the criterion may influence the likelihood of false positives and false negatives. Subjective visual and auditory experiences appear to be similar across humans subjects. The same cannot be said about taste. For example, there
12056-453: The dark, it is most likely because your brain knows what color something is and is relying on that memory. There is some disagreement as to whether the visual system consists of one, two, or three submodalities. Neuroanatomists generally regard it as two submodalities, given that different receptors are responsible for the perception of color and brightness. Some argue that stereopsis , the perception of depth using both eyes, also constitutes
12193-401: The dermis of the skin are examples of neurons that have free nerve endings (1). Also located in the dermis of the skin are lamellated corpuscles , neurons with encapsulated nerve endings that respond to pressure and touch (2). The cells in the retina that respond to light stimuli are an example of a specialized receptor (3), a photoreceptor . A transmembrane protein receptor is a protein in
12330-425: The detection of a stimulus 50% of the time. Absolute threshold is measured by using a method called signal detection . This process involves presenting stimuli of varying intensities to a subject in order to determine the level at which the subject can reliably detect stimulation in a given sense. Differential threshold or just noticeable difference (JDS) is the smallest detectable difference between two stimuli, or
12467-413: The dilator muscle. The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of
12604-466: The direction and location of vibrations picked up through the feet. Studies pertaining to audition started to increase in number towards the latter end of the nineteenth century. During this time, many laboratories in the United States began to create new models, diagrams, and instruments that all pertained to the ear. Auditory cognitive psychology is a branch of cognitive psychology that
12741-411: The directionality of light by the shadow cast by its opaque body. The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of
12878-586: The edge of its shell. It detects moving objects as they pass successive lenses. There is at least one vertebrate, the spookfish , whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals . A compound eye may consist of thousands of individual photoreceptor units or ommatidia ( ommatidium , singular). The image perceived
13015-462: The environment can be either (1) a neuron that has a free nerve ending , with dendrites embedded in tissue that would receive a sensation; (2) a neuron that has an encapsulated ending in which the sensory nerve endings are encapsulated in connective tissue that enhances their sensitivity; or (3) a specialized receptor cell , which has distinct structural components that interpret a specific type of stimulus. The pain and temperature receptors in
13152-445: The environment that affect receptor cell membrane potentials. Other stimuli include the electromagnetic radiation from visible light. For humans, the only electromagnetic energy that is perceived by our eyes is visible light. Some other organisms have receptors that humans lack, such as the heat sensors of snakes, the ultraviolet light sensors of bees, or magnetic receptors in migratory birds. Receptor cells can be further categorized on
13289-422: The eye allows light to enter and project onto a light-sensitive layer of cells known as the retina . The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals which are transmitted to the brain via the optic nerve to produce vision. Such eyes are typically spheroid, filled with the transparent gel-like vitreous humour , possess
13426-412: The eye and spread tears across the cornea to prevent dehydration. These eyelids are also supplemented by the presence of eyelashes , multiple rows of highly innervated and sensitive hairs which grow from the eyelid margins to protect the eye from fine particles and small irritants such as insects. An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at
13563-487: The field of view, such as in rabbits and horses , which have monocular vision . The first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion . The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35 main phyla . In most vertebrates and some molluscs ,
13700-479: The geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye , but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes and different lens crystallins show. The very earliest "eyes", called eye-spots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to
13837-448: The horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point. (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.) Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has
13974-452: The host after entering its body, finally dying inside it. The early-stage larvae do emerge because they must find an unoccupied living host, and the short-lived males must emerge to seek a receptive female in her host. They are believed to be most closely related to beetles , from which they diverged 300–350 million years ago, but do not appear in the fossil record until the mid- Cretaceous around 100 million years ago. The order
14111-482: The host are completely immobile. Virgin females release a pheromone which the males use to locate them. Mating in at least some species is polyandrous , where the female mates with more than one male. In the Stylopidia, the female's anterior region protrudes out between the segments of the host's abdomen. In all strepsipterans the male mates by rupturing the female's cuticle (in the case of Stylopidia, this
14248-444: The host, they undergo hypermetamorphosis and transform into a less-mobile, legless larval form. They induce the host to produce a bag-like structure inside which they feed and grow. This structure, made from host tissue, protects them from the immune defences of the host. Larvae go through four more instars, and in each moult the older cuticle separates but is not discarded (" apolysis without ecdysis "), so multiple layers form around
14385-559: The hot vents, allowing the creatures to avoid being boiled alive. There are ten different eye layouts. Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface. "Simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving
14522-418: The inside in a process known as haemocoelous viviparity . Each female produces many thousands of planidium larvae. The larvae emerge from the brood opening/canal on the female's head, which protrudes outside the host body. Larvae have legs and actively seek out new hosts. Their legs are partly vestigial in that they lack a trochanter , the leg segment that forms the articulation between the basal coxa and
14659-481: The instrument, the listener, and the player of the instrument. Somatosensation is considered a general sense, as opposed to the special senses discussed in this section. Somatosensation is the group of sensory modalities that are associated with touch and interoception. The modalities of somatosensation include pressure , vibration , light touch, tickle , itch , temperature , pain , kinesthesia . Somatosensation , also called tactition (adjectival form: tactile)
14796-591: The larvae. Male larvae pupate after the last moult, but females directly become neotenous adults. The colour and shape of the host's abdomen may be changed and the host usually becomes sterile. The parasites then undergo pupation to become adults. Adult males emerge from the host bodies, while females stay inside. Females may occupy up to 90% of the abdominal volume of their hosts. Adult males are very short-lived, usually surviving less than five hours, and do not feed. Strepsiptera of various species have been documented to attack hosts in many orders, including members of
14933-512: The lateral aspect of the head is known as the auricle . At the end of the auditory canal is the tympanic membrane, or ear drum , which vibrates after it is struck by sound waves. The auricle, ear canal, and tympanic membrane are often referred to as the external ear . The middle ear consists of a space spanned by three small bones called the ossicles . The three ossicles are the malleus , incus , and stapes , which are Latin names that roughly translate to hammer, anvil, and stirrup. The malleus
15070-422: The lens tissue is corrected with inhomogeneous lens material (see Luneburg lens ), or with an aspheric shape. Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens. As mentioned above, a refractive cornea is only useful out of water. In water, there
15207-438: The membrane, and can generate an action potential or a graded potential in the sensory neurons . A third classification of receptors is by how the receptor transduces stimuli into membrane potential changes. Stimuli are of three general types. Some stimuli are ions and macromolecules that affect transmembrane receptor proteins when these chemicals diffuse across the cell membrane. Some stimuli are physical variations in
15344-408: The molecular level, visual stimuli cause changes in the photopigment molecule that lead to changes in membrane potential of the photoreceptor cell. A single unit of light is called a photon , which is described in physics as a packet of energy with properties of both a particle and a wave. The energy of a photon is represented by its wavelength , with each wavelength of visible light corresponding to
15481-437: The movement of hair at the surface of the skin, such as when an insect may be walking along the skin . Stretching of the skin is transduced by stretch receptors known as bulbous corpuscles . Bulbous corpuscles are also known as Ruffini corpuscles, or type II cutaneous mechanoreceptors. The heat receptors are sensitive to infrared radiation and can occur in specialized organs, for instance in pit vipers . The thermoceptors in
15618-403: The muscles of the pharynx contract during swallowing or yawning . Mechanoreceptors turn motion into electrical nerve pulses, which are located in the inner ear. Since sound is vibration, propagating through a medium such as air, the detection of these vibrations, that is the sense of the hearing, is a mechanical sense because these vibrations are mechanically conducted from the eardrum through
15755-450: The orders Zygentoma (silverfish and allies), Orthoptera (grasshoppers, crickets) Blattodea (cockroaches), Mantodea (praying mantis), Heteroptera (bugs), Hymenoptera (wasps, ants and bees), and Diptera (flies). In the strepsipteran family Myrmecolacidae , the males parasitize ants, while the females parasitize Orthoptera. Members of Mengenillidae target Zygentoma exclusively, while Stylopidia targets only winged insects , with
15892-459: The parabolic superposition compound eye type, seen in arthropods such as mayflies , the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp , prawns , crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses. This eye type functions by refracting light, then using
16029-459: The possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity. This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above). Some marine organisms bear more than one lens; for instance
16166-437: The receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source. Through gradual change, the eye-spots of species living in well-lit environments depressed into a shallow "cup" shape. The ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify
16303-513: The refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye. Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera . This type of eye consists of
16440-414: The same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur, is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution. In
16577-714: The sensory organs of the eyes , ears , skin , nose , mouth and the vestibular system . Internal sensation detects stimuli from internal organs and tissues. Internal senses possessed by humans include spatial orientation , proprioception (body position) and nociception (pain). Further internal senses lead to signals such as hunger , thirst , suffocation , and nausea , or different involuntary behaviors, such as vomiting . Some animals are able to detect electrical and magnetic fields , air moisture , or polarized light , while others sense and perceive through alternative systems, such as echolocation . Sensory modalities or sub modalities are different ways sensory information
16714-429: The sister group to the beetle families Meloidae and Ripiphoridae , which have similar parasitic development and forewing reduction. Early molecular research suggested their inclusion as a sister group to the flies , in a clade called Halteria, which have one pair of the wings modified into halteres, and failed to support their relationship to the beetles. Further molecular studies, however, suggested they are outside
16851-494: The skin are quite different from the homeostatic thermoceptors in the brain ( hypothalamus ), which provide feedback on internal body temperature. Strepsiptera The Strepsiptera ( / s t r ɛ p ˈ s ɪ p t ər ə / ) are an order of insects with eleven extant families that include about 600 described species. They are endoparasites of other insects, such as bees , wasps , leafhoppers , silverfish , and cockroaches . Females of most species never emerge from
16988-482: The smallest difference in stimuli that can be judged to be different from each other. Weber's Law is an empirical law that states that the difference threshold is a constant fraction of the comparison stimulus. According to Weber's Law, bigger stimuli require larger differences to be noticed. Magnitude estimation is a psychophysical method in which subjects assign perceived values of given stimuli. The relationship between stimulus intensity and perceptive intensity
17125-402: The source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes. However, the ancestors of modern hagfish , thought to be the protovertebrate, were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it
17262-465: The stimulus. On February 14, 2013, researchers developed a neural implant that gives rats the ability to sense infrared light which for the first time provides living creatures with new abilities, instead of simply replacing or augmenting existing abilities. According to Gestalt Psychology, people perceive the whole of something even if it is not there. The Gestalt's Law of Organization states that people have seven factors that help to group what
17399-423: The surface of the vitreous, which reprocess the hyaluronic acid ), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye. Photoreception
17536-618: The surroundings are light or dark , which is sufficient for the entrainment of circadian rhythms . These are not considered eyes because they lack enough structure to be considered an organ, and do not produce an image. Every technological method of capturing an optical image that humans commonly use occurs in nature, with the exception of zoom and Fresnel lenses . Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates , cephalopods , annelids , crustaceans and Cubozoa . Pit eyes, also known as stemmata , are eye-spots which may be set into
17673-452: The tendency humans have to categorize objects according to past experiences under certain circumstances. If two objects are usually perceived together or within close proximity of each other the Law of Past Experience is usually seen. Hearing, or audition, is the transduction of sound waves into a neural signal that is made possible by the structures of the ear . The large, fleshy structure on
17810-512: The third segment having a lateral process. The family Stylopidae may be paraphyletic . The Elenchidae have two-segmented tarsi and four-segmented antennae, with the third segment having a lateral process. The Halictophagidae have three-segmented tarsi and seven-segmented antennae, with lateral processes from the third and fourth segments. The Stylopidae mostly parasitize wasps and bees, the Elenchidae are known to parasitize Fulgoroidea , while
17947-490: The tips of grass leaves, increasing the chance of being found by strepsipteran males (in the case of females) and putting them in a good position for male emergence (in the case of males). The order, named by William Kirby in 1813, is named for the hindwings , which are held at a twisted angle when at rest (from Greek στρέϕειν ( strephein ), to twist; and πτερόν ( pteron ), wing). The forewings are reduced to halteres . Strepsiptera were once believed to be
18084-587: The transduction of chemical stimuli into electrical potentials. The visual system, or sense of sight, is based on the transduction of light stimuli received through the eyes and contributes to visual perception . The visual system detects light on photoreceptors in the retina of each eye that generates electrical nerve impulses for the perception of varying colors and brightness. There are two types of photoreceptors: rods and cones . Rods are very sensitive to light but do not distinguish colors. Cones distinguish colors but are less sensitive to dim light. At
18221-552: The transparent crystallin protein. Sensory organ A sense is a biological system used by an organism for sensation , the process of gathering information about the surroundings through the detection of stimuli . Although, in some cultures, five human senses were traditionally identified as such (namely sight , smell , touch , taste , and hearing ), many more are now recognized. Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli (such as
18358-425: The two groups are thought to have independently evolved the structures. The hindwings are generally fan-shaped, and have strongly reduced venation . The antennae are flabellate , and are covered in specialised chemoreceptors , likely to detect females over long distances. Adult male Strepsiptera have eyes unlike those of any other insect , resembling the eyes found in the trilobite group Phacopina . Instead of
18495-469: The vertebrates, that were only forced into the photopic environment at a late stage). Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye , and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution , despite their distant common ancestry. Phenotypic convergence of
18632-416: The wavelength scale. The three types of cone opsins , being sensitive to different wavelengths of light, provide us with color vision. By comparing the activity of the three different cones, the brain can extract color information from visual stimuli. For example, a bright blue light that has a wavelength of approximately 450 nm would activate the "red" cones minimally, the "green" cones marginally, and
18769-413: The way that information is encoded, which is similar to the idea of transduction . The main sensory modalities can be described on the basis of how each is transduced. Listing all the different sensory modalities, which can number as many as 17, involves separating the major senses into more specific categories, or submodalities, of the larger sense. An individual sensory modality represents the sensation of
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