Lecture 13

Question 1

Describe the Reichardt detectors

Answer 1

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

Question 2

Describe how the output unit computes stuff

Answer 2

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)

Question 3

Describe the 3 areas involved in motion

Answer 3

• 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

Question 4

What is TMS?

Answer 4

Transcranial magnetic stimulation (TMS) applied to MT in humans disrupts ability to
perceive direction in a random pattern of moving dots

Question 5

Describe the microsimulation study

Answer 5

• 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

Question 6

What is the shortest path constraint?

Answer 6

apparent movement tends to occur along the
shortest path between two stimuli

Question 7

What is biological motion?

Answer 7

self-produced motion of a person or other living organism

• Can help with perceptual organization

Question 8

What is the point light walker stimulus?

Answer 8

created by
placing lights on the joints of a living
organism, which convey their pattern of
movement (and thus, conveys biological
motion)

Question 9

Describe the point light walker study

Answer 9

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

Question 10

What is implied motion?

Answer 10

Implied motion is conveyed by still pictures that depict an action which
involves motion

Question 11

What is representational momentum?

Answer 11

implied motion depicted in a photo can be
‘carried out’, or continue, in the observer’s mind

Question 12

Describe the implied motion study

Answer 12

• In addition to showing completely new pictures, manipulated whether the ‘familiar’ (previously seen)
  pictures were…

1. Exactly the same (control)
2. An image that would have happened slightly
   later than the one they actually saw (time-
   forward condition)
3. An image that would have happened slightly
   earlier than the one they actually saw (time-
   backward condition)

Question 13

Describe the Kourtzi and Kanwisher
(2000)

Answer 13

• fMRI response was measured in middle
  temporal area (MT) and medial superior
  temporal area (MST) in four conditions:

1. Implied motion
2. No-implied motion
3. At rest
4. Houses

• Areas of brain responsible for motion fire
  in response to pictures of implied motion