Sensation and Perception – part 2 (lectures 8 – 13)
Universiteit Utrecht
Lecture 8: Motion perception 3
Motion sensitivity 3
What is motion? 3
Motion detectors 3
Motion types 6
Motion perception 8
Lecture 9: eye movements, the vestibular system and early auditory systems 14
Eye movements in the brain 14
Vestibular system 18
Audition 25
Lecture 10: higher audition 32
Auditory perception 39
Sound segregation and grouping 42
Speech: auditory scene perception 44
Auditory-visual integration 45
Lecture 11: Touch 50
Lecture 12: Olfaction 73
Lecture 13: Gustation (taste) 85
2
,Lecture 8: Motion perception
Motion sensitivity
Every visually guided organism detects motion, but not:
● color
● stereo (depth)
● form
In humans
● 8% of male population congenitally R/G color blind
● depth (stereo vision) doe not work in about 7-10% of people
○ most people become aware of their deficit only when explicitly tested for stereo
vision
Many areas are motion sensitive
● MST, MT V3a, V3, V2, V1
Motion sensitivity = cell has preference for cell that moves vs cell that does not move
-> also preference for particular direction
Motion sensitivity in different species
● There are specific cells for this in retina in rabbits, frogs, more animals
● but not in humans!
Motion sensitivity
● common
● robust
● different mechanisms in different animals
What is motion?
There doesn’t have to be movement of an object to be able to perceive movement
Motion processing is independent of object processing
● there do not have to be changes in the position of the object, as long as the brain sees
motion
Motion detectors
Reichart detector
Reichardt Detectors are hypothetical neural circuits postuated for how the brain can track motion. In
a Reichard detector, a cell in the brain receives input from two receptors in the eye, call them A and
B. The input from A is delayed. If the motion from A to B receptors is timed in such a way that the cell
in the brain recieves the inputs from both A and B at the same time then the cell in the brain will fire.
3
,Light moving from left to right reaches left cone first and then the right cone
However, there is a delay in the first
Less simplified:
Stimulus that stays at the same place: inhibit output
Speed selectivity
A motion neuron can be selective to certain speeds (as with some speeds some light neuron clusters
all reach the motion neuron at the same time and some do not).
● either change the delay;
● or change the span
4
, Thus, if the signals show up at different times -> membrane potential is restored already
● Signals need to reach the collector site before sodium/potassium pump restores the
membrane potential
● small differences from the preferred speed or direction will still work
● tuned responses
Detector Failure
● reichardt detector is based on luminance/color and its matches to inputs -> if inputs change
over time it can't match them
The failure to see motion (to the same degree) suggests we actually use a mechanism like the
Reichart detector.
Detector problems
In this case, the ‘object’ is moving to the right. The
reichardt detector cant detect it, because of the
changing of the luminance all the time.
However, we still see it move.
5
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