Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.
Multimodal perception Multimodal perception is the ability of the mammalian nervous system to combine all of the different inputs of the sensory nervous system to result in an enhanced detection or identification of a particular stimulus. Combinations of all sensory modalities are done in cases where a single sensory modality results in an ambiguous and incomplete result.
Integration of all sensory modalities occurs when multimodal neurons receive sensory information which overlaps with different modalities. Multimodal neurons are found in the superior colliculus; they respond to the versatility of various sensory inputs. The multimodal neurons lead to change of behavior and assist in analyzing behavior responses to certain stimulus. Information from two or more senses is encountered. Multimodal perception is not limited to one area of the brain: many brain regions are activated when sensory information is perceived from the environment. In fact, the hypothesis of having a centralized multisensory region is receiving continually more speculation, as several regions previously uninvestigated are now considered multimodal. The reasons behind this are currently being investigated by several research groups, but it is now understood to approach these issues from a decentralized theoretical perspective. Moreover, several labs using invertebrate model organisms will provide invaluable information to the community as these are more easily studied and are considered to have decentralized nervous systems.
Lip reading Lip reading is a multimodal process for humans. By watching movements of lips and face, humans get conditioned and practice lip reading. Silent lip reading activates the auditory cortex. When sounds are matched or mismatched with the movements of the lips, temporal sulcus of the left hemisphere becomes more active.
Integration effect Multimodal perception comes into effect when a unimodal stimulus fails to produce a response. Integration effect is applied when the brain detects weak unimodal signals and combines them to create a multimodal perception for the mammal. Integration effect is plausible when different stimuli are coincidental. This integration is depressed when multisensory information is not coincidentally presented.
Polymodality Polymodality is the feature of a single receptor of responding to multiple modalities, such as free nerve endings which can respond to temperature, mechanical stimuli (touch, pressure, stretch) or pain (nociception).
Light modality
Description The stimulus modality for vision is light; the human eye is able to access only a limited section of the electromagnetic spectrum, between 380 and 760 nanometres. Specific inhibitory responses that take place in the visual cortex help create a visual focus on a specific point rather than the entire surrounding.
Perception To perceive a light stimulus, the eye must first refract the light so that it directly hits the retina. Refraction in the eye is completed through the combined efforts of the cornea, lens and iris. The transduction of light into neural activity occurs via the photoreceptor cells in the retina. When there is no light, Vitamin A in the body attaches itself to another molecule and becomes a protein. The entire structure consisting of the two molecules becomes a photopigment. When a particle of light hits the photoreceptors of the eye, the two molecules come apart from each other and a chain of chemical reactions occurs. The chemical reaction begins with the photoreceptor sending a message to a neuron called the bipolar cell through the use of an action potential, or nerve impulse. Finally, a message is sent to the ganglion cell and then finally the brain.
Adaptation The eye is able to detect a visual stimulus when the photons (light packets) cause a photopigment molecule, primarily rhodopsin, to come apart. Rhodopsin, which is usually pink, becomes bleached in the process. At high levels of light, photopigments are broken apart faster than can be regenerated. Because a low number of photopigments have been regenerated, the eyes are not sensitive to light. When entering a dark room after being in a well lit area, the eyes require time for a good quantity of rhodopsin to regenerate. As more time passes, there is a higher chance that the photons will split an unbleached photopigment because the rate of regeneration will have surpassed the rate of bleaching. This is called adaptation.
Colour stimuli Humans are able to see an array of colours because light in the visible spectrum is made up of different wavelengths (from 380 to 760 nm). Our ability to see in colour is due to three different cone cells in the retina, containing three different photopigments. The three cones are each specialized to best pick up a certain wavelength (420, 530 and 560 nm or roughly the colours blue, green and red). The brain is able to distinguish the wavelength and colour in the field of vision by figuring out which cone has been stimulated. The physical dimensions of colour include wavelength, intensity and purity while the related perceptual dimensions include hue, brightness and saturation. Primates are the only mammals with colour vision. The Trichromatic theory was proposed in 1802 by Thomas Young. According to Young, the human visual system is able to create any colour through the collection of information from the three cones. The system will put together the information and systematize a new colour based on the amount of each hue that has been detected.
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