'Perceiving the present' as a framework for ecological explanations of the misperception of projected angle and angular size

An implicit, underlying assumption of most Helmholtzian/Bayesian approaches to perception is the hypothesis that the scene an observer perceives is the probable source of the proximal stimulus. There is, however, a nontrivial latency (on the order of 100 ms) between the time of a proximal stimulus and the time a visual percept is elicited. It seems plausible that it would be advantageous for an observer to have, at any time t, a percept representative of what is out there at that very time t, not a percept of the recent past. If this is so, it implies a modification to the implicit hypothesis underlying most existing probabilistic approaches to perception: the new hypothesis is that, given the proximal stimulus, the scene an observer perceives is the probable scene present at the time of the percept. That is, the hypothesis is that what an observer perceives is not the probable source of the proximal stimulus, but the probable way the probable source will be when the percept actually occurs. A model of an observer's typical movements in the world is developed, and it is shown that projected angles are perceived in a way consistent with the way the probable source will project to the eye after a small time period of forward movement by the observer. The predicted and actual direction of projected-angle misperception is sometimes toward 90 degrees and sometimes away from 90 degrees, depending on whether the probable source angle is lying in a plane parallel or perpendicular to the probable direction of motion, respectively. The perception of angular size for lines in a figure with cues they are lying in a plane perpendicular to the direction of motion is also shown to fit the predictions of the model.     

Perceiving the present and a systematization of illusions

Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 × 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller sizes, (2) slower speeds, (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called "perceiving the present," that the visual system possesses mechanisms for compensating neural delay during forward motion. This article shows how this hypothesis predicts the empirical regularity.     

Harnessing vision for computation

Might it be possible to harness the visual system to carry out artificial computations, somewhat akin to how DNA has been harnessed to carry out computation? I provide the beginnings of a research programme attempting to do this. In particular, new techniques are described for building 'visual circuits' (or 'visual software') using wire, NOT, OR, and AND gates in a visual 6modality such that our visual system acts as 'visual hardware' computing the circuit, and generating a resultant perception which is the output.     

Response to briscoe (2010)

In an earlier paper my colleagues and I put forth a theory called "perceiving-the-present" that predicts a systematic pattern across a large variety of illusions, and we presented evidence that the systematic pattern exists. Briscoe puts forth arguments against the theory and the existence of the systematic pattern. Here I provide counterarguments to his criticisms of the theory, and I explain why his arguments do not bear on the existence of the systematic pattern.     

Thirst modulates a perception

Does thirst make you more likely to think you see water? Tales of thirsty desert travelers and oasis mirages are consistent with our intuitions that appetitive state can influence what we see in the world. Yet there has been surprisingly little scrutiny of this appetitive modulation of perception. We tested whether dehydrated subjects would be biased towards perceptions of transparency, a common property of water. We found that thirsty subjects have a greater tendency to perceive transparency in ambiguous stimuli, revealing an ecologically appropriate modulation of the visual system by a basic appetitive motive.     

Latency correction explains the classical geometrical illusions

There is a significant delay between the time when light hits the retina and the time of the consequent percept. It has been hypothesized that the visual system attempts to correct for this latency by generating a percept representative of the way the world probably is at the time the percept is elicited, rather than a percept of the recent past. Here we show that such a 'perceiving the present' hypothesis explains a number of classical geometrical illusions: the Hering, Orbison, Müller-Lyer, Double Judd, Poggendorff, Corner, and Upside-down-T illusions. Each stimulus is perceived as it would project in the next moment were the observer moving through the scene the stimulus probably represents. We also examine one general class of predictions made by the hypothesis, and report psychophysical experiments confirming the predictions.     

Economically organized hierarchies in WordNet and the Oxford English Dictionary

Good definitions consist of words that are more basic than the defined word. There are, however, many ways of satisfying this desideratum. For example, at one extreme, there could be a small set of atomic words that are used to define all other words; i.e., there would be just two hierarchical levels. Alternatively, there could be many hierarchical levels, where a small set of atomic words is used to define a larger set of words, and these are, in turn, used to define the next hierarchically higher set of words, and so on to the top-level of very specific, complex words. Importantly, some possible organizations are more economical than others in the amount of space required to record all the definitions. Here I ask, How economical are dictionaries? I present a simple model for an optimal set of definitions, predicting on the order of seven hierarchical levels. I test the model via measurements from WordNet and the Oxford English Dictionary, and find that the organization of each possesses the signature features expected for an economical dictionary.     

Function identification from noisy data with recursive error bounds

New success criteria of inductive inference in computational learning theory are introduced which model learning total (not necessarily recursive) functions with (possibly everywhere) imprecise theories from (possibly always) inaccurate data. It is proved that for any level of error allowable by the new success criteria, there exists a class of recursive functions such that not all f are identifiable via the criterion at that level of error. Also, necessary and sufficient conditions on the error level are given for when more classes of functions may be identified.