retinal / visual information

Question 1

Rushton (2007)

Answer 1

• tested flow parsing hypothesis
• visual search and simulated head movement
• neurons in visual cortex specialised to detect characteristic patterns of retinal motion associated with self-movement (Wurtz 1998) i.e. “optic flow detectors”
• identify and parse out this motion so any motion left on retina due to externally-moving object in scene
• as with stationary head, visual search time with simulated moving head does not increase with number of objects i.e. still “pops out”
• however: optic flow detectors use disparity info to identify motion patterns
• so on same task but with no disparity info = longer RTs in simulated head movement condition as function of no. of elements i.e. no longer pops out
• without disparity info, flow parsing is not able to subtract out motion from self-movement

Question 2

Wurtz 1998

Answer 2

found neurons in visual cortex specialised to detect characteristic patterns of retinal motion associated with self-movement i.e. “optic flow detectors”

Question 3

Warren & Rushton (2009)

Answer 3

• typical pattern of retinal motion when walking down a hall
• stationary walls etc have retinal motion to need to globally subtract expansion field
• retinal motion of falling ball is oblique, so need to compensate for this and add motion to location of ball so will perceive it as falling vertically (recover its physical trajectory)
• viewed radial expansion flow fields and a moving probe
• if probe was on left, the global component of leftward motion is subtracted from the probe motion, so perceived trajectory tilts rightward
• strong evidence for purely visual mechanism mainly using a global subtraction process, with only small contributions due to local motion contrast mechanisms (seen because effect was maintained even when probe was in hemifield without global expansion pattern)

Question 4

Eifuku & Wurtz (1999)

Answer 4

• single-cell recordings in primate brain
• dorsal part of MST specialised for optic flow caused by self-movement
• ventrolateral part of MST specialised for analysis of object motion in a scene

Question 5

Warren & Hannon (1988)

Answer 5

• radial patterns of optic flow used to perceive direction of self-motion and to guide locomotion

(but Warren and Rushton 2009 now argue optic flow does much more than this! is used to detect external object movement in scene so important motion cue)

Question 6

Rushton (2018)

Answer 6

• optic flow, form and position cues provided conflicting info for separating out retinal motion due to object movement and retinal motion due to self-movement
• e.g. when positional cue altered polarity it appeared to be moving in opposite direction, and gave conflicting cue to the one optic flow gave
• found that flow parsing relies on optic flow alone (only flow cues influence perceived probe movement)
• so primary role of neural network that processes optic flow is to identify scene-relative object movement
• only relies on single cue - seems counterintuitive as higher precision comes from combining cues. but may be that we favour speed in these circumstances?

Question 7

Royden & Holloway (2014)

Answer 7

• computational model using response properties of speed- and direction-tuned cells in primate visual cortex can identify borders of moving objects in a scene where the observer is moving
• provides valid theoretical explanation to psychophysical results

Question 8

Wilkie & Wann (2003)

Answer 8

• accuracy of steering affected by whether driver can make free eye movements or is required to fixate

Question 9

Royden & Connors (2010)

Answer 9

• can detect moving object in radial optic flow field based on 2D direction of motion (if it differs enough from the radial patten generated by self-movement, it will be detected)
• threshold for detection increased as duration of presentation or no. of items in scene decreased
• thresholds sig higher when asked to detect moving object in deformation pattern

Question 10

Kornmuller

Answer 10

• paralyse eye muscles (effectors can’t carry out eye movement)
• try to look right = perception of world jumping to the right
• intended but unfulfilled eye movement = efference copy not cancelled out, but transmitted to higher centres in the brain and results in conscious perceptual experience

Question 11

Bender (2012)

Answer 11

• reduced lateralised sensorimotor activation in schizophrenia patients immediately preceding movement

Question 12

Lindner (2005)

Answer 12

• Sz and delusions of influence (someone else responsible for action)
• manipulation of stimuli during pursuit eye movements results in perception of movement of environment more readily in SZ than in controls
• delusions correlated with how much they attributed sensory consequences of own eye movement to external environment

Question 13

Pynn (2013)

Answer 13

• attenuated processing of reafference signals
• failure to disambiguate self-induced from externally generated sensory input may cause +ve symptoms e.g. hallucinations
• dysfunction in neural comparator