extraretinal / non-visual information Flashcards
1
Q
Von Holst (1954): LANDMARK
A
- optomotor / righting reflex in fly = stationary fly in rotating drum will turn itself in direction of drum rotation
- fly which rotates left in drum doesn’t turn back to right, despite same pattern of retinal motion
- efference copy from motor cortical areas matches efference signal coming from effector. appropriate compensation
- inappropriate compensation when fly’s head is rotated 180 degrees i.e. prediction of motor movement doesn’t match actual motor signal = positive feedback loop
- OM reflex in invertebrates caused by statoliths applying force on sensory organ i.e. labyrinth (human analogue is ultricle and saccule (otoliths) in inner ear, help form vestibular system)
- can increase force artificially in the lab, so make statoliths heavier = lessens righting reflex as smaller tilts seem to produce same effect
- shows re-afference signal produced by labyrinth is not blocked during self-movement (reflex theory) as the signal has quantitative effect on degree of reflex
- greater reafference = smaller reflex movement (appropriate compensation for self-movement)
- reafference signal / predicted sensory consequences of movement account for eye movements when pursuing moving object
2
Q
Wallach (1974)
A
- compensation for lateral head translation = perceived object rotation
- gain of +/-0.45 tolerated before Ps reported ball moving (bias)
- background had little effect
- no forced choice
- didn’t measure psychometric functions such as thresholds, just bias
3
Q
Tcheang (2005)
A
- studied ability to detect rotation of a ball during self-movement
- target-alone condition had large +ve bias of 25-45% i.e. when perceived as stationary, ball was actually moving towards them
- cue-rich condition i.e. background = only 5% bias
- thresholds relatively small (so actually quite precise)
- thresholds for discrimination were also reduced for cue rich, as well as biases
- used psychometric functions for both thresholds and biases (unlike Wallach)
- e.g. proportion of trials ball was reported to have moved “with” P plotted against rotation gain of ball = bias (shift in 50% point) shows rotation gain where subject perceived ball as stationary
- relative motion between static cues and moving objects is important perceptual cue, shown by condition w/background
- suggested that biases were due to mis-estimation of distance walked
- thorough psychophysical methods e.g. psychometric functions for bias, threshold etc
- more flexibility for observer movement
can dissociate object and observer movement more easily
4
Q
Wexler (2003)
A
- task involving use of allocentric spatial info
- better performance (reduced bias) during voluntary rather than passive movement
- voluntary motion plays important role in visual perception of 3D object motion and shape etc
- ERS important: motion signals (re-afference copy/corollary discharge)
- proprioceptive info from sensory feedback during movement (vestibular, somatosensory)
- proprioceptive / vestibular info available during both active and passive so motor signals from head motion must play large role in allocentric representation of space during movement
- large bias (0.4) but low thresholds (0.1)
bias smaller and sensitivity higher during voluntary movement
5
Q
Skavenski (1972)
A
- head stabilised, can only move eyes
- consciously aware of eye position info due to proprioception / inflow signals, and this info could be used to control eye position in the dark
- e.g. eyes moved slightly by experimenter. participant could correctly report direction etc and also make appropriate eye movements in order to bring eye back to original position
6
Q
Freeman + Banks (1998)
A
- filehne illusion = perceive stationary object as moving when making eye movement
- thought to be result of ERS underestimating eye velocity
- altered size of RS by manipulating spatial frequence of grating
- increased RS (higher spatial freq) = more weighting given to external object as opposed to head movement (ERS), so perceive illusory motion in direction of pursuit (against ERS)
- decreased spatial freq = reduced RS so more weight given to ERS, perceive movement in opposite direction to pursuit i.e. direction of ERS (reversed filehne illusion)
7
Q
Brindley + Merton (1960)
A
- curare / partial paralysis then try to move eyes = objects appeared to move due to intact reafference copy
- full paralysis + eyes moved with forceps + no visual cues = couldn’t detect passive eye movements due to no reafference copy (not making movements themselves) and no exafference info due to muscle paralysis
8
Q
Stevens (1976)
A
- full paralysis + attempt to move eyes to right. although eyes felt paralysed the visual world seemed to jump to the right (intact reafference copy)
- “displacement” of visual scene, not actual movement
- perception due to corollary discharge from extraocular muscles
9
Q
Sherrington 1918
A
inflow (afferent) = motor feedback due to proprioceptive info from muscle expansion and contraction
10
Q
Helmholtz 1850
A
outflow (efferent) = copy of motor command released from motor cortex provides automatic sensory feedback and provides expectations of movement
11
Q
Freeman (2010)
A
- explains motion illusion with use of bayesian prior
- smooth pursuit eye movement illusions: pursued objects appear slower (Aubert-Fleishl illusion), stationary objects appear to move (Filehne illusion) etc
- presence or absence of eye movement is paramount in driving differences in precision of estimates
- extra-retinal info (proprioception, efference copies of eye speed etc) is less reliable than retinal info, so more influenced by prior assumption that movement is zero
- so speed of pursued stimuli perceived as slower
- argue that two separate bayes estimates needed: one for pursued stimuli and one for fixated stimuli
12
Q
Warren & Rushton (2009)
A
- 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)
- so optic flow not just implicated in heading and locomotion, but crucial for recovery of external object motion
13
Q
Wurtz (1999)
A
- 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
14
Q
Warren & Hannon (1988)
A
radial patterns of optic flow used to perceive direction of self-motion (heading direction) and to guide locomotion
15
Q
Rushton (2007)
A
- 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
