Chapter 3 Flashcards
lateral inhibition
inhibition transmitted across the retina (limulus experiment - crabs - can stimulate individual receptors - a light in A produced a large response, a light in B diminished response in A due to inhibition transmitted across lateral plexus)
ommatidia
limullus eye made up of hundres of ommatidia, each has a small lense on surface of they eye directly over a receptor
lightness
proportino of shades ranging from white to black
The Herman Grid
3 x 3 black boxes with gray ‘ghost’ spots that are not physically present. DIAGRAM FOR INHIBITION EXPLANATION
simultaneous contrast
perception of brightness/colour of one area is affected by presence of an adjacent/surrounding area (identical grey looks different surrounded by lighter and darker colours - lighter background = more lateral inhibition making grey look darker - dark background causes less firing of neurons and therefore less inhibition)
White’s illusion
Not explained by lateral inhibition, example of belongingness- appearance is influenced by the area to which it appears to belong. In white’s illusion, A appears to be behind the bars and B appears on them DIAGRAM
optic nerve
made up of axons of retinal ganglion cells
Receptive field
Region of retina over which a cell in the visual system can be influenced by light (excitation/ihibition) as demonstrated by Hartline - isolated single fibre in the optic nerve in open eye cup of frog by teasing it apart where it leaves the eye and recorded from this nerve while shining light on the retina - it responded only to a small area
centre surround organization
study of response in optic nerve fibres in cats found that receptive fields are organized in a centre-surround organization (centre responds differently than surround), shows that neurons may respond best to particular patterns of illumination
excitatory area
spot of light increases firing
inhibitory area
spot of light decreases firing
centre surround antagonism
neuron responds best to light the size of excitatory centre, larger light decreases firing as it enters inhibitory portion
Lateral geniculate nucleus
oval body located at the termination of optic tract on each side of the brain and acts as the primary relay center for visual information received from the retina of the eye, also receives feedback that helps determine input
Hubel and Wiesel’s research on receptive fields
found that neurons at higher levels of visual system become more tuned to respond best to more and more specific stimuli (anaesthetized animal’s eyes focused on a screen w glasses so that image on screen would be on back of eye, eyes stayed stationary, found that points on screen correspond to points on retina)
visual receiving area
occipital lobe where signals from retina first reach cortex - also called striate cortex due to striped appearance in cross section
superior colliculus
receives some signals from eye (10%, 90 % to LGN) and plays role in movement of eyes
simple cortical cells
cells in striate cortex with excitatory and inhibitory fields side by side
orientation tuning curve
relationship between orientation and firing determined by measuring responses of simple cortical cells to bars of light with different orientations
complex cells
respond best to moving, bar like stimuli with specific orientation (across entire field)
end stopped cells
fire to moving lines of specific length or moving corners/angles
feature detectors
simple, complex and end stopped cells
stimulus physiology relationship
neurons respond to oriented lines
physiology perception relationship
link between physiology and perception
selective adaptation
neurons tuned to a specific property fire- causes fatigue and adaptation causing decreased rate of firing and reduced reaction when stimulus immediately presented again; selective because only neurons tuned to fire adapt
contrast threshold
minimum intensity difference between two adjacent bars that can just be detected - to measure, determine contrast threshold, adapt person to one orientation by having them view high contrast adapting stimulus and remeasure (should be more difficult to see dim grating)
selective rearing
animals reared in environment with only certain types of stimuli - neurons that respond to this stimuli more prevalent
neural plasticity/experience dependent plasticity
response properties of neurons can be shaped by perceptual experience (long term as opposed to selective adaptation which is short term) - kitten stripes experiment
Inferotemporal cortex
Gross - removing parts of IT in monkeys affected their ability to recognize objects - recorded from single neuron in IT and presented various stimuli over 3-4 day periods, found neurons that respond only to complex stimuli
prosopagnosia
Humans with IT damage unable to recognize faces
fusiform face area
underside of temporal lobe in humans, responds to faces
sensory coding
how firing of neurons represents various characteristics of the environment (1 neuron - specificity coding, groups - group coding)
specificity coding
proposes a particular object is represented by firing of a neurone that responds only to that and no other object(s)
grandmother cell
neuron that fires to one specific stimulus (unlikely)
distributed coding
representation by patterns of firing in a large number of neuron (evidence in all senses but usually large numbers are unneccesary)
sparse coding
representation by patterns of firing by small group of neurons with majority remaining silent
