Lecture 13 Flashcards
Describe the Reichardt detectors
A Reichardt detectors is a model of a simple neural circuit that could fire in response to
movement in one direction
- Neuron A and neuron B each send signals to the output unit, which ‘compares’ the signals
it receives from those two neurons to determine whether they are synchronized (i.e. received
at exactly the same time) - The signal that is sent from neuron A to the output unit
goes through the delay unit, which slows down the
speed of transmission of the signal (to the output unit) - If the timing is just right, the output units receives a
signal from both neuron A and B at exactly the same
time, and motion is perceived
Describe how the output unit computes stuff
It multiplies the signal it receives from
neurons A and B at any one discreet point in time to ‘decide’ whether or not to fire
- If those signals reach the output unit together = motion detected
- Because a number > 0, when multiplied by another number that is also > 0,
results in a value > 0 (and the neuron fires if the value it calculates is > 0) - If those signals do not reach the output unit at the same time, then no motion is
detected - Because 0, when multiplied by any number > 0, still results in a value = 0 (and
the neuron does not fire if the value it calculates
=
0)
Describe the 3 areas involved in motion
- Perception of motion begins in striate cortex
(V1), the region of the occipital lobe where
information from the retinas first reach the
cortex - Complex cortical cells (in V1) respond to
movement of the ends of objects - Middle temporal area (MT) implicated in other
aspects of motion perception
What is TMS?
Transcranial magnetic stimulation (TMS) applied to MT in humans disrupts ability to
perceive direction in a random pattern of moving dots
Describe the microsimulation study
- Microstimulation experiment Britten et al. (1992):
- Monkey trained to indicate direction of fields of moving dots
- Neurons in MT cortex that respond to specific direction were activated using microstimulation, which shifted their judgment to the artificially
stimulated direction
What is the shortest path constraint?
apparent movement tends to occur along the
shortest path between two stimuli
What is biological motion?
self-produced motion of a person or other living organism
- Can help with perceptual organization
What is the point light walker stimulus?
created by
placing lights on the joints of a living
organism, which convey their pattern of
movement (and thus, conveys biological
motion)
Describe the point light walker study
Grossman and Blake (2001): participants
determined whether motion was biological
or scrambled while being scanned (fMRI)
- Used point-light walker stimuli with noise
added to dots to reduce performance to
71% accuracy - Superior temporal sulcus (STS) more
active for biological motion - Other studies show activation in response
to biological motion in FFA and PFC that
contain mirror neurons
Grossman et al. (2005) found TMS applied to
superior temporal sulcus (STS) decreased the
participants’ ability to detect biological motion
What is implied motion?
Implied motion is conveyed by still pictures that depict an action which
involves motion
What is representational momentum?
implied motion depicted in a photo can be
‘carried out’, or continue, in the observer’s mind
Describe the implied motion study
- In addition to showing completely new pictures, manipulated whether the ‘familiar’ (previously seen)
pictures were…
- Exactly the same (control)
- An image that would have happened slightly
later than the one they actually saw (time-
forward condition) - An image that would have happened slightly
earlier than the one they actually saw (time-
backward condition)
Describe the Kourtzi and Kanwisher
(2000)
- fMRI response was measured in middle
temporal area (MT) and medial superior
temporal area (MST) in four conditions:
- Implied motion
- No-implied motion
- At rest
- Houses
- Areas of brain responsible for motion fire
in response to pictures of implied motion
