PSY2061 Chapter 6-7: PSY2061 - Readings - Week 5 - Sensory Systems
5 Jun 2018
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PSY2061- Readings – Week 5 – Sensory Systems
~ visual systems
• pupil and lens
•
o irises - regulate the amount of light reaching the retinas
o light enters the eye through the pupil - the hole in the iris
o sensitivity - the ability to detect the presence of dimly lit objects
o acuity - the ability to see the details of objects
o the adjustment of pupil size in response to changes in illumination
represents a compromise between sensitivity and acuity
o accomodation - the process of adjusting the configuration of the
lenses to bring images into focus on the retina
• eye position and binocular disparity
•
o binocular disparity
o
▪ the difference in the position of the same image on the two
retinas
▪ greater for close objects than for distant objects
• the retina and translation of light into neural signals
•
o after light passes through the pupil and the lens - it reaches the
retina
o the retina converts light to neural signals, conducts them toward
the CNS and participates in the processing of the signals
o structure of the retina
o
▪ composed of five different types of neurons
▪
▪ receptors
▪ horizontal cells
▪
▪ lateral communication
▪ bipolar cells
▪ amacrine cells
▪
▪ specialised for lateral communication -
communication across the major channels of
sensory input
▪ retinal ganglion cells
▪ retina is inside out
▪
▪ light reaches the receptor layer after passing
through the other four layers
▪ once the receptors have been activated, the neural
message is transmitted back out through the retinal
layers to the retinal ganglion cells, whose axons
project across the outside of the retina before
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gathering together in a bundle and exiting the
eyeball.
▪ This inside-out arrangement creates two visual
problems:
▪
▪ One is that the incoming light is distorted by
the retinal tissue through which it must pass
before reaching the receptors.
▪ The other is that for the bundle of retinal
ganglion cell axons to leave the eye, there
must be a gap in the receptor layer; this gap is
called the blind spot.
▪ first of the problems is minimised by the fovea
▪
▪ fovea - an indentation at the centre of the retina -
specialised for high acuity vision
▪ reduces the distortion of incoming light
▪ blind spot
▪
▪ minimised by completion
▪ the visual system uses information provided by the
receptors around the blind spot to fill in the gaps in
retinal images
▪ surface interpolation
▪
▪ the process by which we perceive surfaces -
the visual system extracts information about
edges and from it infers the appearance of
large surfaces
• cone and rod vision
•
o two different receptors in the human retina
o duplexity theory of vision - cones and rods mediate different kinds
of vision
o
▪ photopic vision
▪
▪ cone mediated vision
▪ predominates in good lighting and provides high
acuity
▪ scotopic vision
▪
▪ rod mediated vision
▪ dim illumination
• spectral sensitivity
•
o spectral sensitivity curve - a graph of the relative brightness of
lights of the same intensity presented at different wavelengths
o
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▪ photopic spectral sensitivity curve
▪ scotopic spectral sensitivity curve
o wavelength as a substantial effect on the perception of brightness
o purkinje effect
• eye movement
•
o eye continually scan the visual field
o our visual perception at any instant is a summation of recent visual
information
o temporal integration
o involuntary fixation eye movements
o
▪ tremor
▪ drifts
▪ saccades
▪ eye movements enable us to see during fixation by keeping
the images moving on the retina
• visual transduction - the conversion of light to neural signals
•
o transduction
o
▪ the conversion of one form of energy to another
▪ visual transduction
▪
▪ the conversion of light to neural signals by the visual
receptors
▪ rhodopsin - a g-protein coupled receptor that responds to
light faster than to neurotransmitter molecules
▪
▪ rhodopsin receptors initiate a cascade of
intracellular chemical events when they are
activated
• from retina to primary visual cortex
•
o retina-geniculate-striate pathways - which conduct signals from
each retina to the primary visual cortex via the lateral geniculate
nuclei of the thalamus
o retina-geniculate-striate system
o
▪ 90% of retinal ganglion cells become part of the retina-
geniculate-striate pathways
▪ all signals from the left visual field reach the right primary
visual cortex - either ipsilaterally from the temporal
hemiretina of the right eye or contra laterally from the nail
hemiretina of the left eye
o retinotopic organisation
o
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