Sensory Modalities

Vision

  • One of the most important sensory modalities in humans


  • Enables remote sensing and has evolutionary advantages as we can detect sth before being in direct contact with it

The eye

  • The visual stimulus is light which activates the visual system
  • the visual sense organ that collects, amplifies and filters visual stimuli
  • also contains photoreceptors that aid transduction
  • Transduction = light --> electrical signaling

Retina

two photoreceptors

Rods (Rhodopsin) which are more sensitive and used in low light vision

Cones = has 3 subtypes responding to different wavelengths and are concentrated in the fovea

medium green

long red

Short blue

Receptive Field

  • aspect of the external world that produces a change in firing rate of a given sensory cell
  • arises due to convergence which increases deeper into the visual system
  • all visual system neurons after the ganglion cells have a receptive field

Ganglion cells

on centre, off surround = more active when light falls in the centre of the receptive field

off centre, on surround = more active when light falls on the outer periphery

  • exhibits centre surround organisation of their receptive fields and contains 2 main kinds
  • which allows detection of changes in stimuli between 2 parts of the receptive field (lateral inhibition)

Neural Pathways

visual field --> eyes --> optic nerve, chiasm then tract --> LGN in the thalamus --> primary visual cortex

the primary visual cortex contains detectors from a convergence of ganglion cells, and 3 types of other cells like

Info from the right visual field enters the left hemisphere of the brain and vice versa

simple cells = lines in a particular region of space

complex cells = line wherever they are in space

hypercomplex cells = lines of a certain length

Colour = a psychological property

contains 3 dimensions

saturation = purity of a colour

lightness = if a colour is light or dark

hue = apparent colour of an object

Audition = where sound waves is the auditory stimulus

Although colour perception is similar across cultures, the labels for colours differ

trichromatic theory = colour is explained by differential activation of 3 colour receptors in the eye

opponent process theory= colours are derived from activity of 3 antagonistic systems

sound waves can vary in

amplitude

complexity

frequency

transduction = vibrations in the oval window --> cochlear fluid --> basilor membrane where the sensory receptors are

Olfaction = where odorants is the olfactory stimulus

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