Spatial Vision - Terminology Flashcards Preview

PSY247 - Perception Psychologty > Spatial Vision - Terminology > Flashcards

Flashcards in Spatial Vision - Terminology Deck (31):
1

What are Complex Cells?
Where are they located?
What do they respond too?

Type of V1 cell.
Respond to an oriented stimulus anywhere within their receptive field.

2

Contralateral?
What is the contralateral eye?

Contralateral = taking from the opposite.
Contralateral eye - taking input from the eye on the opposite side of the body (this happens in layers 1, 4 & 6 in the LGN.

3

What is the Contrast sensitivity function?

The contrast sensitivity function comes from plotting the contrast threshold function which plots spatial frequency on the x-axis and threshold on the y-axis.
We plot the % of correct answers using a two alternative forced choice method.By doing so, the graph shows a lopsided U shape.

REMEMBER - Threshold is the opposite of sensitivity.
Therefore, we divide by one to yield the contrast sensitivity function. (This is an upside down lopsided U). Now we replace the y-axis with sensitivity. This allows us to determine if someone sees high spatial frequency or low spatial frequency patterns.

4

What are Gratings?

Patterns of light and dark bars, widely used in vision research. They often have a sinusoidal luminance profile. (They fade from white to black back to white).

5

What is a Hemifield? What

A hemifeld is 170 degree range of vision that is seen by one eye that is focusing straight ahead. The image that is projected onto the retina (for each eye) can be cut down the middle, with the fovea/macula defining the centre. Therefore, you have two halves of the retina, a left half and a right half.

6

What is the Herman Grid?

How does the Herman Grid illusion work?

Herman grid illusion. A grid of evenly spaced black square boxes. Dark patches are perceived at the intersections, even though they are not there. The illusion is less noticeable closer to the fovea.
Consider two ON centre cells.
They both have identical stimulation when one is at the cross intersection and the other is in between two squares.
However, the cell at the cross intersection receives more light in its inhibitory surround. Therefore, more inhibition Hence why dark patches are seen at the cross-section between the squares.
Note, when receptive fields are too small or the intersections are too large the illusion does not work.

7

What is a Hypercolumn?

Where is it located?
What is its purpose?

A hypercolumn is in V1 when columns of cells that have preferential firing to 180 degrees of stimulus orientation and take input from both eyes.
A hypercolumn informs you almost everything you would want to know about a small area of visual space.

8

What are Hypercomplex cells?

Type of cell found in V1
Will respond to an orientated stimulus anywhere within their receptive field, but prefer stimuli with an end that is within their receptive field.
They are known as 'end-stopped'. (Sometimes two ends).

9

Ice cube model

The ice cube model describes the organisation of V1 cortical tissue. It assumes that V1 can be arranged in orderly cubes in which all information from one part of the visual field is processed.

10

Illusory contours

Occur when we detect edges that aren't really there.

11

Magnocellular

Occur in the first two area's of the LGN.
- Large receptive fields (low resolution)
- Fast responding
- High sensitivity
- Part of motion processing (cells almost colour blind)

12

Michelson contrast

Is the contrast formula.
Constrast = (Lmax-Lmin) / (Lmin+Lmax)
Contrast formula gives you an answer between 0 and 1.
1 = high contrast, 0 = greyscale (no contrast)
Contrast is the difference in physical luminance, taking into account overall luminance levels.

13

Lateral antagonism

A.K.A. Centre-surround antagonism, spatial opponency, lateral inhibition.
The ganglion cell receptive field has two concentric area's (circular areas).
Either ON or OFF centre.
- Tells you where changes in the image occur
- Allows us to compensates for the intensity of a light source

14

Ocular dominance columns

Ocular dominance columns are a column of cells that preferentially fire to the same stimulus AND take input from the same eye.

15

Orientation column

Orientation columns are a column of cells that have the same preferred stimulus orientation.

Orientation columns are how V1 is organised.

16

Orientation tuning

A cell will respond preferentially to an edge or bar, of a specific orientation wthin its selected field.
Peak activity at preferred stimulus. Activity drops to create curve as stimulus changes from the preferred orientation.
The range of orientations that a cell fires at is its bandwith.
Small bandwith = sharp tuniing
Large bandiwth = broad tuning

17

Oblique effect

The relative deficiency we have for perception for oblique contours compared to verticle or horizontal ones.

18

Cortical magnification

More cortex devoted to the fovea - where vision is more precise.

19

Simple cells

Type of V1 cell.
Respond to an orientated stimulus in a particular location within their receptive field.
They can be bar detectors or edge detectors.

20

How are simple cells built?

Simple cells can be built from the outputs of retinal ganglion cells (with centre-surround antagonism). If you vertically lineup the LGN cells (either OFF or ON) with an "AND" gate. The receptive field translates to a V1 cell. Essentially, V1 is a representation of the sum of ganglion cells.

21

How are complex cells built?

Complex cells can be built from connecting several simple cells, that all have the same orientation preference. They would contain different edge locations. Are connected with an "OR" operation.

22

Orientation tuning

A cell will respond preferentially to an edge or bar, of a specific orientation wthin its selected field.
Peak activity at preferred stimulus. Activity drops to create curve as stimulus changes from the preferred orientation.
The range of orientations that a cell fires at is its bandwidth.
Small bandwidth = sharp tuning
Large bandwidth = broad tuning

23

Tilt aftereffect

The tilt aftereffect occurs when we have a prolonged exposure to tilted bars and then subsequently we look at verticle bars. The verticle bars appear to tilt in the opposite direction of the first-seen tilted bars.

24

Periphery

Our ability to see objects and movement outside the direct line of vision. (This is due to cells located outside the macula/fovea).

25

Spatial frequency aftereffect

Spatial frequency aftereffect is the same as the tilt aftereffect. Think of it as size aftereffect. This tells us that there is also a population code for size.
E.g. If we adapt to fat stripes and then look at medium stripes, the after effect will make the medium stripes look thinner then they really are.

26

Spatial frequency tuning

S

27

Snellen acuity

A snellen acutiy chart is a that can be used to measure visual acuity.

28

Spatial frequency tuning

What are the cells tuned to?

What is high spatial frequency?
What is low spatial frequency?

Spatial frequency tuning is preferential tuning of cells to certain spatial frequncies. Spatial frequencies are encoded through population coding.
Cells are tuned to;
- Spatial frequency
- Phase
- Orientation
- Contrast
*Think like sine waves

High spatial frequency = thin stripes
Low spatial frequency = fat stripes

29

Square wave

Square waves can be added togher, and by doing so you can create a square wave with sharp edges.

30

How are gratings measured?

Gratings are measured in cycles (i.e. dark to light) per degree of visual angle (cdp or deg-1).
Essentially, how many peaks and troughs can you fit into 1 degree on your retina.

31

What are the negatives of using a Snellen chart for testing visual acuity?

What would be a better testing method?

- Only tests high contrast
- No information is given about thresholds for low and medium spatial frequencies.
- It's easy to cheat

A better testing method would be to measure the contrast sensitivity function