PA 5 Flashcards
During single cell recording measuring ganglion response, Before anything is put on the screen, the ganglion cell is already..
active, i.e there is baseline activity
A (ganglion cell) cells receptive field is the area
what are the two regions in this area, what do they do
area on the retina which, when stimulated by light, elicits a change in the firing rate of the cell.
Excitatory,
inhibitory response -decrease in firing response
two types of centre-surround antagonism (ganglion cells)
ON-centre OFF-surround (central photoreceptor = excitatory of ganglion cell, Surrounding = inhibitory)
OFF-centre ON-surround (opposite)
Why have this centre-surround antagonism (ganglion cells) organisation?
Ganglion cells respond to changes in light falling within receptive field
(e.g. if there is an area of dark and area of light indicating a boundary/edge)
Ideal for detecting spots of light & edges
NOT able to detect orientation of bars
No response to changes in overall level of illumination
Ganglion cells reduce the amount of information in a stimulus by finding
contours and boundaries
tilt after affect what is it
stare for prolonged period of time at tilted (adapting) pattern. Then look at vertical (test) pattern.
The vertical lines are perceived to be tilted in opposite direction
expl for tilt after effect 3 components
- Orientation tuned neurons respond best to preferred orientation but also to other similar orientations.
- Perceived orientation determined by distribution of responses across cells (match will be excited most, but similar will be next most. Or if oriented between 3 and 4, they will be both excited. This pattern of distribution across all cells is what matters)
- Adaptation - Cell’s response deceases following prolonged activity.
do u get more or less of a tilt after affect when the adapt condition is closer to the test condition
More when closer as is more overlap
cats and monkey single cell recordings show orientation lines with different line sizes and for different orientations.
How have we studied this in humans
Tilt after effects
and size after effects
spatial frequecy
number of bars per unit distance (usually cycles per degree) degree as in retinal degree
has bars get thinner, you can fit more cycles in the unit distance. So you get higher spatial frequency
my expl of tilt after effect
for the test condition, let’s say you have a distribution of cells 1,2,3,4,5,6.
The orientation of the line is best suited to 4. and slightly suited to 3,5. These cells will adapt and become less responsive.
When an orientation with similar orientation is shown, it will require some of the cells that have adapted, but because those cells are less responsive, the distribution will shift in the opposite direction.
Therefore, the test lines will be perceived to be orientated in the opposite direction of the adapt stimulus
high contrast
big differences in luminance between the areas of light and dark
spatial contrast sensitivity function
we have greater sensitivity to intermediate spatial frequencies. They can be perceived at low contrasts.
We have lower sensitivity to to high and low spatial frequencies. They need higher contrasts to be perceived.
retinal vs real size
spatial frequency
spatial frequency tells us ab size on retina. Does NOT tell us ab size in real world.
Projected size depends on distance
