Independent and parallel visual processing of ensemble statistics: Evidence from dual tasks
Authors: Vladislav A Khvostov
Igor S Utochkin
Journal: Journal of Vision (2019)
Discipline: CLINICAL MEDICINE
Keywords: visual system; ensemble summary statistics; object numerosity; mean; feature variance
Affiliations: National Research University Higher School of Economics, Moscow, Russian Federation.

Abstract:  The visual system can represent multiple objects in a compressed form of ensemble summary statistics (such as object numerosity, mean, and feature variance/range). Yet the relationships between the different types of visual statistics remain relatively unclear. Here, we tested whether two summaries (mean and numerosity, or mean and range) are calculated independently from each other and in parallel. Our participants performed dual tasks requiring a report about two summaries in each trial, and single tasks requiring a report about one of the summaries. We estimated trial-by-trial correlations between the precision of reports as well as correlations across observers. Both analyses showed the absence of correlations between different types of ensemble statistics, suggesting their independence. We also found no decrement (except that related to the order of report explained by memory retrieval) in performance in dual compared to single tasks, which suggests that two statistics of one ensemble can be processed in parallel. 

Retracted: No

PubPeer comments:
 In the spirit of the  online journal club which PubPeer was designed to be, I would appreciate if the authors could try to clarify certain of their concepts and statements, in light of what appear to me to be apparent logical contradictions. To begin with, I call attention to the following statements:  The visual system can represent multiple objects in a compressed form of ensemble summary statistics (such as object numerosity, mean, and feature variance range)...the visual system has to compress the big and often redundant amount of visual information received from the environment. My confusion has to do with my understanding of the visual process as beginning with point information; with individual photons, reflected from surfaces in the environment, entering the pupil and striking, to begin with, individual photoreceptors. As attempts to achieve vision on the basis of somehow correlating these individual points (the principle of AI) have shown us, and as studies of perception (the Gestalt literature) had already shown, this point information is in itself rather uninformative and insufficient. In the famous words of G. Kanizsa, vision needs to go  beyond the information given. In other words, the  visual information received from the environment, *far from needing to be reduced*, actually needs to be transformed - with the emphasis on  formed. Points to 3D objects, via segregating, grouping, filling in, etc. The process is by nature inferential, in the sense that, again, it cannot be a direct consequence of the  raw data. So the idea that the visual process first constructs, then reduces, information seems awkward to me. Are the authors saying that the *constructed* visual percept, is secondarily pruned? They say in their introduction that reduction occurs in order to  overcome the severe restrictions of the processing bottleneck associated with the limited capacity of attention and working memory. At the same time, they are implying that this reduction applies to the visual percept itself (as when the say  the visual system can represent multiple objects in compressed form ...). Their method of ascertaining and discussing the consequences of this presumed reduction also implies we re dealing with visual facts.  Object means, for example, are apparently supposed to be features of the percept itself. Again, this seems paradoxical, since  objects must first be constructed and then, presumably,  reduced. I would appreciate if the authors could expand on this a little more and point out possible errors in my train of thought. I, as well as another commenter, have expanded on what I see as the many paradoxes of the  ensemble statistics point of view in a comment on Cohen, Dennett Kanwisher (2016). The second commenter found my concerns to be valid, saying:  I found Lydia s criticism to be very valuable, it clearly points the focus on  single fixations when perception is certainly a sequence of such fixations. Once I accepted that, I found it hard to support the reasoning and speculation in the paper. The brief presentations employed by K and U limit the number of fixations by viewers; and this raises the question whether this artificially produces results that seem to conform with their hypothesis. We have not gotten any response from those authors. Perhaps Khvostov and Utochkin will be more helpful. ,