abstract Postdiction effects are phenomena in which a stimulus influences the appearance of events taking place before it. In metacontrast masking, for instance, a masking stimulus can ren- der a target stimulus shown before the mask invisible. This and other postdiction effects have been considered incompatible with a simple explanation according to which (i) our perceptual experiences are delayed for only the time it takes for a distal stimulus to reach our sensory receptors and for our neural mechanisms to process (...) it, and (ii) the order in which the processing of stimuli is completed corresponds with the apparent temporal order of stimuli. As a result, the theories that account for more than a single postdiction effect reject at least one of these theses. This paper presents a new framework for the tim- ing of experiences—the non-linear latency difference view—in which the three most dis- cussed postdiction effects—apparent motion, the flash-lag effect, and metacontrast masking—can be accounted for while simultaneously holding theses (i) and (ii). This view is grounded in the local reentrant processes, which are known to have a crucial role in perception. Accordingly, the non-linear latency difference view is both more parsimonious and more empirically plausible than the competing theories, all of which remain largely silent about the neural implementation of the mechanisms they postulate. (shrink)

Paul Churchland's book is an entertaining and instructive advertisement for a "neurocomputational" vision of how the brain works. While we agree with its general thrust, and commend its lucid pedagogy on a host of difficult topics, we note that such pedagogy often exploits artificially heightened contrast, and sometimes the result is a misleading caricature instead of a helpful simplification. In particular, Churchland is eager to contrast the explanation of consciousness that can be accomplished by his "aspiring new structural and dynamic (...) cognitive prototype: recurrent PDP networks" with what strikes him as the retrograde introduction by Dennett of a virtual von Neumannesque machine--a "failed prototype"--as the key element in an explanation of human consciousness. We will try to show that by oversimplifying Dennett's alternative, he has taken a potential supplement to his own view--a much needed supplement--and transformed it in his imagination into a subversive threat. In part 1, we will expose and correct the mistaken contrasts. In part 2, we will compare the performance of the two views on Churchland's list of seven features of consciousness any theory must account for, showing that Dennett's account provides more than Churchland has recognized, and indeed offers answers to key questions that Churchland's account is powerless to address. At that point, Churchland's project and Dennett's could be seen to collaborate in a useful division of labor instead of being in mortal combat, were it not for what appears to be a fairly major disagreement about consciousness in non-human animals. Part 3 briefly examines this issue. It may be due to a misunderstanding, which when cleared up might restore the happy prospect of unification. (shrink)