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(NAS Colloquium) Vision From Photon to Perception (1999) / Chapter Skim
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Motion perception: Seeing and deciding
Pages 72-77

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From page 72...
... Our ultimate goal is to understand how perceptual dec~s~ons are formed in the context of this visual discrimination task. Perceptual Decisions To investigate the neural basis of a simple decision process, we employed a psychophysical task that links the sensory representation of motion direction to the motor representation of saccadic eye movements.
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From page 73...
... The motion signals originate in large part from columns of directionally selective neurons in extrastriate visual areas MT and MST (20~. This laboratory has shown that single neurons in MT and MST are remarkably sensitive to the motion signals in our displays, that inactivation of MT selectively impairs performance on this task, and that electrical stimulation of a column of directionally selective cells can bias a monkey's decisions toward the direction encoded by the stimulated column (21-27~.
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From page 74...
... For our purposes, however, it was necessary to demonstrate that these neurons remain predictive in a fundamentally different task in which the monkey chooses among saccade targets contingent upon a visually based decision process. The critical issue now before us is to determine whether the responses of LIP neurons provide insight concerning the decision process per se or whether the predictive activity can be explained trivially as the result of purely sensory or purely motor signals.
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From page 75...
... Just as clearly, however, the two dashed curves lie closer to each other than do the two solid curves, showing that LIP neurons do not predict the decision as well on error trials as on correct trials. Again, this pattern of activity would not be expected of a strictly motor signal, since the required eye movement is the same for all trials represented by the two green curves (saccades to T1)
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From page 76...
... A Look at the Future If the effort to identify neural substrates of a decision process is ultimately successful, a host of fascinating questions will be brought into the realm of physiological investigation. If, for example, LIP integrates motion signals to form a plan to move the eyes in our psychophysical task, a precise pattern of circuitry must exist between the direction columns in MT and MST and the movement fields of LIP neurons.
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From page 77...
... (1991) in The Neural Basis of Visual Function, ed.
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Key Terms

  • lip neurons
  • coherent motion
  • predictive activity
  • decision process
  • delay period

  • eye movement
  • saccadic eye
  • discrimination task
  • eye movements
  • error trials

  • motion signals
  • random dot
  • neural basis
  • motor signals
  • movement fields

  • dot stimulus
  • neural activity
  • lip neuron
  • sensory signals
  • motion direction

  • forced choice
  • firing rate
  • strictly motor
  • stimulus strength
  • direction discrimination

  • correct choices
  • unprecedented opportunities
  • solid lines
  • sensory representation
  • period activity


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