Motion

Question 1

Rotating snake illusion

Answer 1

Better at detecting high contrast versus low contrast changes

Question 2

Waterfall illusion

Answer 2

Visual illusion at moving scene (waterfall) for several seconds then look at stationary scenes (rock) cause the still scene to appear as if its moving in the opposite direction

-neural fatigue causality

We can see motion even in the absence of any movement

Mechanism = neurons tuned for opposite direction are relatively more active, causing illusion of reverse motion

Characteristics:
- directionality = illusory movement is opposite to original stimulus
- duration = lasts a few seconds
- variants = rotating spirals and moving text

Question 3

Tiltaftereffect

Answer 3

Must be a place code for motion direction

Left go right
Up go down
Down go up

Question 4

Apparent motion

Answer 4

We have frames and not see timing and space are all important to produce motion

Visual illusion of movement created when stationary objects are presented in rapid succession
Brain interprets changing as continuous motion = contracting sequence of images

Question 5

Movement detector

Answer 5

Delay and compare model

• scheme developed in 50s by Reinhardt to explain flight of beetle

Direction-selective motion arises from simple, nondirectional photoreceptors

Receptors AandB different locations, signal from one receptor delayed by low-pass filter and other isn’t
Delayed signal is multiplied instantaneously
Signal arrives at the same time the delayed B signal causing high output. Signals dont coincide, causing low output.

Question 6

Kinematograms

Answer 6

QR code where small segment is changed
Braddock 1974, 80

• subjects tried to identify the orientation of a moving area of dots

Type of visual stimulus used in vision research to study how the brain processes motion,

Question 7

Kinematograms two methods

Answer 7

AM detected two methods
1. Short range process (SRP) relying on response of low-level motion detectors
2. LRP - cogntive process that tracks features from 1 position to another

Only possible with small displacement, time intervals, present pattern to same eye

Question 8

Direction selective cells

Answer 8

All animals tested such direction selective cells are found

Frogs - early papers show that they do not reposnd to stationary targets, but they have cells in retina that fire to moving blobs EARLY FOR FROGS IN RETINA

Monkey (humans) - no directionally selective cells found in retina or LGN. Some cells in V1 are directionally selective (those fed by magnocellular division of LGN) LATER FOR US

Question 9

Visual areas

Answer 9

MT - middle temporal area also known as V5
- specialised extrastriate cortical region crucial for visual percpetion

Located in posterior bank of the superior temporal sulcus (primates)

Located in surface of the brain (humans)

Question 10

Direction selective cell area -
MT

Answer 10

snowden et al, 1992
Neurons in area MT show strong directional slectivity

Here the neuron responds strongly to motion down to the left

Question 11

^x in space and in time

Answer 11

Mikami, Newsome & Wurtz 1986

Neurons reposne of single MT neurons to series of flashes (apparent motion) occurring within their receptive fields

MT neurons highly sensitive for the direction and speed of motion

Receptive fields allow for directional interactions over long distances from neurons V1

Evidence for speed opponent mechanisms showing how MT recat differently to a spot of light depending on its speed relative to their preferred speed

Question 12

Human MT - imaging studies

Answer 12

Middle temporal cortex crucial,
Specialised cortical region responsible for processing motion information

• speed direction, 3D motion in depth

Primary visual cortex V1, highly sensitive to moving patterns, significantly contributions from dorsal and right ventral visual pathways

Question 13

What does the visual area contain

Answer 13

High concentration of direction-selective neurons that process the speed and direction of moving stimuli, forming a key component of the dorsal where/how pathway

Question 14

MT neural selectivity

Answer 14

Neurons with MT are highly selective for motion direction, speed and binoculars disparity

Question 15

Deleta T Deleta x

Answer 15

Time between flash and distance between the flash,

Movement null movement

Question 16

Anatomical position located within the dorsal stream

Answer 16

Receive direct input from V1 (primary visual cortex) and V@, projects to the MST (medial superior temporal area

Often studied using fMRI

Question 17

Damage to the MT

Answer 17

Can cause Akinestopsia - rare motion-blindness disorder where patients struggle to percieve motion

Question 18

How strong is MT selectivity

Answer 18

Approximately 86% in area show strong selectivity for the direction of motion

Arranged in vertical columns spanning 400-500 microns with adjacent columns

Question 19

MT functional types

Answer 19

Contain a continuum of direction-selective cells, ranging component direction-selective (CDS) cells to Pattern Direction-Selective (PDS) cells

Question 20

Peripheral vision emphasis

Answer 20

MT and MTc the fovea is represented ventocausally, while the visual field periphery is represented dorsorotrally

Question 21

Development and origin of MT

Answer 21

While direction selectivity in the retina is present early, cortical direction selectivity in MT is thought to be largely inherited from V1, both areas shows similar limitations on directional responses

Question 22

Directional interactions temporal and spatial limits

Answer 22

Maximum spatial interval was 3x as large in MT than in V1.
Maximum temporal interval was similar in MT and V1, did not vary with receptive field size or eccentricity

Question 23

Human imaging MT

Answer 23

Resonance imaging - fMRI

Equilinance responses = fMRI activty in human MT decreases at near equiluminance, which matches electorphysiological results from macaque MT regarding motion perception

Question 24

Egnima patten

Answer 24

V5 activation - perception of motion in the egnima figure is casually linked to the activation of v5/mt

Question 25

Brain mechanism of v5

Answer 25

When viewing the static enigma figure, the increase in regional cerebral blood flow occurs in the V5, which is responsible for processing real motion

Question 26

Role of microsaccades

Answer 26

Illusory motion is driven by microsaccades (small eye movements) during visual fixation. Increase in teh rate of these eye movements often precede the perception of faster illusory motion

Question 27

Time course of the V5

Answer 27

Activation and subsequent perception of the illusion often involve a delay, with studies showing interfering V5/MT just before viewing can disrupt the illusion for approximately 400ms

Question 28

Cerebral akinetopsia

Answer 28

Motion blindness - extremely rare neurological disorder, often caused by lesions in cortical area V5 Caused by damage to visual cortex often due to strokes, tumor’s, trauma Discontinuous motion = moving objects appear freezes or stop action jumping from one position to another Invisibility motion = might seem to disappear or become hazy when they move L.M most celebrated patient = Zihl et al 1983.

Question 29

Key aspects of cerebral akinetopsia

Answer 29

Paietnst may see moving objects as a series of still images to a strobe light or cinema reel effect, for example pouring tea may be seen as frozen Neurological basis - disorder from damage to visual v5 (part of teh extrastriate cortex), which is responsible for detecting and processing directional visual motion

Question 30

Braddick

Answer 30

Powerful tool is vision research designed to study motion perception by isolating it from form recognition Certain percentage of dots move coherently in a single direction in subsequent frame, while others move randomly (noise) allowing researchers to test the limits of visual processing

Question 32

Motion perception 1993

Answer 32

Zeki, watson and frackowiak - PET scans view visual stimuli and static stimuli comparing conditions V5 (MT) showed increased activty when participants saw motion, located within visual cortex She;cicely activated by motion, not just general visual input. Function specialisation in the brain, brain actively processes motion and not eyes. Explains motion perception disorders

Question 34

Visual fog

Answer 34

1998 snowden - o investigate how visual conditions like fog affect perceived speed whilst driving Diving simulator, drive at specific speeds in different weather conditions Findings: - fog increased, perceived themselves as going faster than actually were, reduced their speed less than needed, drove faster in fog. Fog reduced visual contrast and detail (optic flow), brain uses motion cues to judge speed, fewer cues -> speed is underestimated Speed perception heavily on visual information form the environment

Question 35

Motion key concepts

Answer 35

- motion aftereffects - apparent motion = short range process - motion detector = delay and compare model - area MT(V5) - motion blindness (cerebral akinetopsia) - speed perception

Question 36

Delay and compare model

Answer 36

Motion perception by comparing inputs from two adjacent retinal receptors