Zenon Pylyshyn

��In four experiments we address the question whether several visual objects can be selected voluntarily (exogenously) and then tracked in a Multiple Object Tracking paradigm and, if so, whether the selection involves a different process. Experiment 1 showed that items can indeed be selected based on their labels. Experiment 2 showed that to select the complement set to a set that is automatically (exogenously) selected — e.g. to select all objects not flashed — observers require additional time and that given 1080 ms they were able to select and track them as well as those selected automatically. Experiment 3 showed that the additional time needed in the previous experiment cannot be attributed solely to time required to disengage attention from the initially automatic selections. Experiment 4 showed that the added time provides a monotonically greater benefit when there are more targets, suggesting a serial process. These results are discussed in relation to the Visual Index (FINST) theory which assumes that visual indexes are captured by a data-driven process. It is suggested that voluntarily allocated attention can be used to facilitate the automatic attention capture by objects of interest.

This study investigates a new experimental paradigm called the Modified Traveling Salesman Problem. This task requires subjects to visit once and only once n invisible targets in a 2D display, using a virtual vehicle controlled by the subject. Subjects can only see the directions of the targets from the current location of the vehicle, displayed by a set of oriented segments that can be viewed inside a circular window surrounding the vehicle. Two conditions were compared. In the “allocentric” condition, subjects see the vehicle move across the screen and change orientation under their command. The “egocentric” condition is similar except for how the information is provided: the position and orientation of the vehicle icon remains fixed at the center of the screen and only target directions, as indicated by the oriented segments, change as the subject “moves” the vehicle. The unexpected finding was that this task can be performed, in either condition, for up to 10 targets. We consider two possible strategies that might be used, a location-based strategy and a segment strategy. The location-based strategy relies on spatial memory and attempts to infer the locations of all the targets. The segment strategy is more local and focuses on the directional segments themselves, keeping track of the ones that represent already-visited targets. A number of observations suggest that the segment strategy was used, at least for larger numbers of targets. According to our hypothesis, keeping track of the segments requires one to use indexical reference for associating the segments with their status in the task - given by current status predicates Visited or Not-visited -, perhaps using visual indexes, deictic pointers, or object files.

In the past decade there has been renewed interest in the study of mental imagery. Emboldened by new findings from neuroscience, many people have revived the idea that mental imagery involves a special format of thought, one that is pictorial in nature. But the evidence and the arguments that exposed deep conceptual and empirical problems in the picture theory over the past 300 years have not gone away. I argue that the new evidence from neural imaging and clinical neuropsychology does little to justify this recidivism because it does not address the format of mental images. I also discuss some reasons why the picture theory is so resistant to counterarguments and suggest ways in which non-pictorial theories might account for the apparent spatial nature of images.

Although the study of visual perception has made more progress in the past 40 years than any other area of cognitive science, there remain major disagreements as to how closely vision is tied to general cognition. This paper sets out some of the arguments for both sides and defends the position that an important part of visual perception, which may be called early vision or just vision, is prohibited from accessing relevant expectations, knowledge and utilities - in other words it is cognitively impenetrable. That part of vision is complex and articulated and provides a representation of the 3-D surfaces of objects sufficient to serve as an index into memory, with somewhat different outputs being made available to other systems such as those dealing with motor control. The paper also addresses certain conceptual and methodological issues, including the use of signal detection theory and event-related potentials to assess cognitive penetration of vision. A distinction is made among several stages in visual processing. These include, in addition to the inflexible early-vision stage, a pre-perceptual attention allocation stage and a post-perceptual evaluation, memory-accessing, and inference stage which provide several different highly constrained ways in which cognition can affect the outcome of visual perception. The paper discusses arguments that have been presented in both computer vision and psychology showing that vision is "intelligent" and involves elements of problem solving". It is suggested that these cases do not show cognitive penetration, but rather they show that certain natural constraints on interpretation, concerned primarily with optical and geometrical properties of the world, have been compiled into the visual system. The paper also examines a number of examples where instructions and "hints" are alleged to affect

Marr (1982) may have been one of the rst vision researchers to insist that in modeling vision it is important to separate the location of visual features from their type. He argued that in early stages of visual processing there must be “place tokens” that enable subsequent stages of the visual system to treat locations independent of what specic feature type was at that location. Thus, in certain respects a collinear array of diverse features could still be perceived as a line, and under certain conditions could function as such in perceptual phenomena like the Poggendorf illusion

Using the Multiple Object Tracking (MOT) task, Pylyshyn & Leonard (VSS03) showed that a small brief probe dot was detected more poorly when it occurred on a nontarget than when it occurred either on a target or in the space between items, suggesting that moving nontarget items were inhibited. Here we generalize this finding by comparing probe detection performance against a baseline condition in which no tracking was required. We examined both a baseline condition in which objects did not move and one in which they moved exactly as in the probe detection task, but without tracking. Detection in the nonmoving control was essentially error-free, but probe detection performance in the moving (non-tracking) control task did depend on the probe location. Nonetheless, the findings reported earlier (worse detection on nontargets than anywhere else) remained after we took account of the baseline performance (using several different baseline comparison methods). Using this new baseline-control method we also showed that inhibition does not spread more than about 1.3 degrees of visual angle from the nontargets as the latter move during a tracking trial. In the present report we also describe some preliminary studies of conditions under which enhancement of targets, as well as inhibition of nontargets, may be obtained. Increasing the number and type of nontargets appeared to improve the detection of probes on targets, relative to baseline. However, we failed to find evidence that potentially distracting nontarget objects were inhibited more than clearly task-irrelevant objects, as would be expected if inhibition were a top-down process applied in order to improve performance on the main tracking task. For example, using the comparison with its matching baseline, we showed that task-irrelevant stationary items (which are never confused with targets in the tracking task) appeared to be inhibited even more than nontargets.

It is argued that the traditional distinction between artificial intelligence and cognitive simulation amounts to little more than a difference in style of research - a different ordering in goal priorities and different methodological allegiances. Both enterprises are constrained by empirical considerations and both are directed at understanding classes of tasks that are defined by essentially psychological criteria. Because of the different ordering of priorities, however, they occasionally take somewhat different stands on such issues as the power/generality trade-off and on the relevance of the sort of data collected in experimental psychology laboratories

This paper argues that a theory of situated vision, suited for the dual purposes of object recognition and the control of action, will have to provide something more than a system that constructs a conceptual representation from visual stimuli: it will also need to provide a special kind of direct (preconceptual, unmediated) connection between elements of a visual representation and certain elements in the world. Like natural language demonstratives (such as `this' or `that') this direct connection allows entities to be referred to without being categorized or conceptualized. Several reasons are given for why we need such a preconcep- tual mechanism which individuates and keeps track of several individual objects in the world. One is that early vision must pick out and compute the relation among several individual objects while ignoring their properties. Another is that incrementally computing and updating representations of a dynamic scene requires keeping track of token individuals despite changes in their properties or locations. It is then noted that a mechanism meeting these requirements has already been proposed in order to account for a number of disparate empiri- cal phenomena, including subitizing, search-subset selection and multiple object tracking (Pylyshyn et al., Canadian Journal of Experimental Psychology 48(2) (1994) 260). This mechanism, called a visual index or FINST, is brie

Jacques Mehler was notoriously charitable in embracing a diversity of approaches to science and to the use of many different methodologies. One place where his ecumenism brought the two of us into disagreement is when the evidence of brain imaging was cited in support of different psychological doctrines, such as the picture-theory of mental imagery. Jacques remained steadfast in his faith in the ability of neuroscience data (where the main source of evidence has been from clinical neurology and neuro-imaging) to choose among different psychological positions. I personally have seen little reason for this optimism so Jacques and I frequently found ourselves disagreeing on this issue, though I should add that we rarely disagreed on substantive issues on which we both had views. This particular bone of contention, however, kept us busy at parties and during the many commutes between New York and New Jersey, where Jacques was a frequent visitor at the Rutgers Center for Cognitive Science. Now that I am in a position where he is a captive audience it seems an opportune time to raise the question again

People have always wondered how thinking takes place and what thoughts are constructed from. We typically experience our thoughts as involving pictorial (or sensory) contents or as being in words. Although this idea has been enshrined in psychology as the “dual code” theory of reasoning and memory, serious questions have been raised concerning this view. It appears that whatever the form of our thoughts it is unlikely that it is anything like our experience of them. But if thought is not in pictures or words, what form does it take? If we do not sometimes think in words, then what actually goes on when we think by engaging in an “inner dialogue”? And if we do not sometimes think in pictures, what goes on when we reason by creating and examining “mental images”?