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Jeroen Goossens, Joke Kalisvaart, Roohollah Massoudi, Peter Bremen; The primacy effect in primate saccade target selection. Journal of Vision 2017;17(10):1168. doi: 10.1167/17.10.1168.
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It is often assumed that decision-making involves neural competition, accumulation of evidence 'scores' over time, and commitment to a choice once its 'scores' reach decision-threshold first. So far, however, neither the first-to-threshold rule, nor the nature of competition, has been revealed by experiments. Here, we presented two simultaneously-flashed targets that reversed their intensity difference during presentation, and instructed subjects to saccade towards the brightest target. Both humans (n=6) and monkeys (n=2) preferentially chose the target that was brightest during the first stimulus phase. Unless this first phase was too short, primacy persisted even if the second, reversed-intensity phase lasted longer. This effect did not result from premature commitment to the initially-dominant target; a strong target imbalance in the opposite direction later on drove nearly all responses towards that location. Moreover, there was a non-monotonic relation between primacy and target imbalance; increasing this imbalance beyond 40 cd/m2 caused an attenuation of primacy.These are the hallmarks of hysteresis, predicted by models in which target-representations compete through strong feedback. Preliminary analysis indicates that the choice behavior is reflected in the timing of visual burst activity of neurons in the Frontal Eye Field; bursts for 'winning' target-representations preceded the 'losing' ones. However, the contrast-dependent changes in burst timing did not result from cross-inhibition; keeping the intensity of the target inside the receptive field of the cell constant while changing the intensity of the opponent target, abolished the latency changes.
Meeting abstract presented at VSS 2017
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