Suppression and facilitation of motion perception in humans: a reply to Schallmo & Murray (2018)

TL;DR

This paper defends previous computational and psychophysical analyses of motion perception experiments against critiques, emphasizing the role of divisive normalization over inhibition and clarifying data interpretation.

Contribution

It provides a detailed rebuttal to critiques, reaffirming the original analysis of motion perception mechanisms and emphasizing the importance of divisive normalization in explaining psychophysical results.

Findings

Divisive normalization explains motion perception effects.

Critiques do not invalidate original analysis.

Modeling applies broadly to similar experimental designs.

Abstract

In a recent publication (Tzvetanov (2018), bioRxiv 465807), I made an extensive analysis with computational modelling and psychophysics of the simple experimental design of Dr. D.Tadin (Tadin, Lappin, Gilroy and Blake (2003), Nature, 424:312-315) about motion perception changes in humans due to size and contrast of the stimulus. This publication sparked from strong claims made in Schallmo et al. (2018) (eLife, 7:e30334) about two important points: (1) "divisive normalization", not inhibitory and excitatory mechanisms, creates the observed psychophysical results and (2) drug-enhanced inhibition showed perceptual outcomes that hint to "weaker suppression" (i.e. inhibition) not stronger "suppression". Schallmo & Murray (2018, bioRxiv, 495291) presented concerns about my extensive publication, specifically about the parts where I directly analysed some of their methods, results and claims. Here, I show that their concerns do not provide clear answers to my specific points and further do not mention other major critiques of data interpretation and modelling of this experimental design. Therefore, I maintain all my claims that were elaborated in details in my first publication (Tzvetanov, 2018, bioRxiv 465807): the specific ones that analyse the results of their and other studies, but also the more broad modelling that is applicable to any study using the simple experimental design of Dr. D.Tadin.