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Comment on “Single-trial spike trains in parietal cortex reveal discrete steps during decision-making”

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Science  25 Mar 2016:
Vol. 351, Issue 6280, pp. 1406
DOI: 10.1126/science.aad3242

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  1. Fig. 1

    Experimental evidence in support of a gradual accumulation of evidence in LIP. (A) LIP neurons ramp, on average, during an RT task. Averages are sorted by RT quantile (color), using trials in which the monkey chose the direction associated with the choice target in the neuron’s response field. [Modified from (2), showing responses from ~200 ms after stimulus onset; see also figure 2, B and D, in (11)]. (B) LIP neurons undergo multiple incremental changes in firing rate on single trials. On this example trial, the monkey decided in favor of the green target in the neuron’s response field, consistent with the accumulated evidence from the sequence of shapes [from movie 3 of (4)]. [For more single-trial examples, see the movies in (4) and movies 1 and 2 in (5). For population analyses, see (4, 5)].

  2. Fig. 2 Behavioral integration times are difficult to determine from the analyzed data set but are certainly shorter than the full 500- to 1000-ms viewing durations.

    Open circles correspond to behavioral data obtained after the collection of the neural recordings [figure 7D in (12)]. Smooth curves show fits of a bounded diffusion model, from which we estimate the median decision time to be ~250 ms across all motion strengths [methods explained in (13, 14)]. The neural data analyzed by Latimer et al. (1) accompanied the behavioral data shown by the filled stars [from figure 7A of (12)]. Accuracy was unaffected by viewing duration over the range tested, and overall performance was markedly poorer in this data set. [Data are from figure 7, A and D, in (12), with missing coherences kindly supplied by Latimer et al.]