Sources of noise during accumulation of evidence in unrestrained and voluntarily head-restrained rats.
Benjamin B. Scott*, Christine M. Constantinople*, Jeffrey C. Erlich, David W. Tank and Carlos D. Brody, eLife2015
Many models of decision-making process include an “evidence accumulation” stage: evidence for or against different options is gradually accumulated over time, and it is the result of that accumulation process that drives the final decision. In these models (including work from our own lab), it is usually assumed that noise from inputs at different timepoints is independent of each other, in which case the total variance would increase linearly with the number of inputs. But is that true? Using a visual flashes accumulation task, we found that the data was better described by a model in which variance increased as the square of the number of inputs. In other words, the standard deviation scales linearly with the number of inputs, similar to “scalar variability” models used for numerical and time interval estimation. This result held both for freely moving rats and for head-restrained rats; the latter suggests the phenomenon can be investigated using cellular-resolution two-photon microscopy.