Properties of Shape Tuning of Macaque Inferior Temporal Neurons Examined Using Rapid Serial Visual Presentation. De Baene, Premereur, Vogels. J Neurophysiology 2007.

  1. Examined macaque inferior temporal cortical neuron responses to parametrically defined shapes
  2. “we found that the large majority of neurons preferred extremes of the shape configuration, extending the results of a previous study using simpler shapes and a standard testing paradigm. A population analysis of the neuronal responses demonstrated that, in general, IT neurons can represent the similarities among the shapes at an ordinal level, extending a previous study that used a smaller number of shapes and a categorization task. However, the same analysis showed that IT neurons do not faithfully represent the physical similarities among the shapes.”
  3. Also, IT neurons adapt to stimulus distribution statistics
  4. “Single IT neurons can be strongly selective for object attributes such as shape, texture, and color, while remaining tolerant to some transformations such as object position and scale”
  5. Rapidly display images in succession without interstimulus break
  6. Other results also show that neurons seem to be tuned to activate at when shapes that come from the extremes of parameter shape are presented
  7. “Because a high number of stimuli are presented repeatedly in RSVP, this paradigm might be more sensitive to adaptive effects than classical testing paradigms in which one stimulus is presented per trial after acquisition of fixation and the intertrial interval is relatively long”
  8. <Skipping experimental details and moving on to results>
  9. <Again,> Neuron responses were tuned to extremes of the parameter space and not normally or uniformly distributed
    1. They used a number of different shape classes, and all showed this effect
  10. There was “a good overall fit between physical and neural similarities.”
  11. Although they had the issue that some dimensions were more salient than others,
  12. Screen Shot 2015-08-04 at 1.11.39 PM
  13. Did a hierarchical clustering of shapes according to neural responses and different shape classes are always together (aside from one shape class that is split in half and has another shape class “inside” it)
  14. “One issue to consider regarding the interpretation of the observed stronger responses for extreme stimuli is that the employed stimuli are likely to be suboptimal for the tested IT neurons. The critical question here is why the extreme stimuli are less suboptimal than the other stimuli given the likely high-dimensional space in which IT neurons are tuned. A satisfactory answer to this important question will require a full description of the nature of the tuning functions of IT neurons as well as knowledge about the relative position and range of the stimulus set with respect to these tuning functions. The possibility cannot be excluded that IT neurons learn the stimulus statistics of the parametric shape spaces and thus that the observed tunings depend on the stimulation history and the specific stimulus spaces. Experiment 2 demonstrated that the responses of IT neurons can indeed be modified by changes in input statistics. These effects were small in comparison to the degree of monotonic tuning, but stimulus statistics might exert a more profound effect with more extensive daily repetition of the same stimulus spaces as is the common practice in singlecell recording experiments  The MDS results clearly show that IT neurons are more sensitive for some stimulus variations (e.g., indentation; stimulus sets 3 and 4) than for others. This is in agreement with previous studies using calibrated sets of shapes…”

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