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Heida M. Sigurdardottir, David L. Sheinberg; Origins of Shape Selectivity in the Lateral Intraparietal Area (LIP). Journal of Vision 2010;10(7):942. doi: 10.1167/10.7.942.
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© ARVO (1962-2015); The Authors (2016-present)
Recent evidence indicates that LIP is sensitive to object shape. To further explore this shape selectivity, two monkeys were trained on arbitrary shape-action associations, where a centrally presented shape was associated with a saccade to or away from an LIP neuron's response field. Each day the monkeys learned the meaning (to or from RF) of four novel shapes, and were retrained on four previously learned old shapes. In a second task, the monkeys simply viewed the shapes. This passive task established that LIP neurons indeed responded selectively to certain shapes, even meaningless novel shapes. The shape selectivity, however, did not seem to be invariant to changes in location. The shape-action association task revealed an interaction between novelty (old vs. novel shapes) and meaning (to vs. from RF). Somewhat surprisingly, early in the trial, novel ‘to RF’ shapes showed a lower response than ‘from RF’ shapes. The old shapes showed the opposite pattern, with initial ‘to RF’ responses higher than ‘from RF’ responses. The effect for old stimuli quickly reversed again so that ‘to RF’ responses became lower than ‘from RF’ responses. Finally, when the monkeys were allowed to saccade, both old and novel stimuli had higher responses in the ‘to RF’ condition, but the difference was more pronounced for old shapes. These results suggest that LIP shape selectivity is unlikely to be part of a representation of object structure, because it should be little affected by meaning. That the meaning of the shapes can affect even the earliest LIP responses raises the possibility that they reflect a best guess of how to react to an object. Even novel shapes have points of interest that may bias looking patterns. With extensive training, as in the case of old shapes, these initial responses may be overridden to represent an arbitrarily associated action.
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