Response to Comment on "Single-trial spike trains in parietal cortex reveal discrete steps during decision-making"

Abstract

Shadlen et al's Comment focuses on extrapolations of our results that were not implied or asserted in our Report. They discuss alternate analyses of average firing rates in other tasks, the relationship between neural activity and behavior, and possible extensions of the standard models we examined. Although interesting to contemplate, these points are not germane to the findings of our Report: that stepping dynamics provided a better statistical description of lateral intraparietal area spike trains than diffusion-to-bound dynamics for a majority of neurons.

Fig 1:

(A) Monkey’s accuracy as a function of stimulus duration during neurophysiological recording sessions (dots) from (5) overlaid with the theoretical curves (solid lines) obtained from a maximum likelihood fit of a DDM. The median durations of behavioral integration under this model are 408, 362, and 152 ms across the range of motion strengths shown. These integration times are in fact longer than those recently reported in (10). A modest lapse rate in the DDM accounts for the asymptotic performance slightly below 100% [e.g.,(7,8,15] The other monkey (not discussed by Shadlen et al.) exhibits similar signatures of substantial evidence accumulation. (B) This animal’s behavior is also very similar to that of previous studies. Dependency of accuracy on viewing duration and motion strength [same conventions as in (A)] from a purely behavioral data set collected from the same monkey (5) (grayscale dots) using a range of shorter durations that closely match those used in a previous study (6) (colored dots). The data from the two studies are very similar (i.e., they overlap and follow matching forms), demonstrating that our monkey achieves performance on the random dots task nearly identical to that reported in a study by some of the authors of Shadlen et al.