No abstract

There are many celebrated examples of ambiguous perceptual configurations such as the Necker cube that abruptly and repeatedly ''switch'' among possible perceptual states. When such ambiguous configurations are presented intermittently, observers tend to see the same perceptual state on successive trials. The outcome of each trial apparently serves to ''prime'' the outcome of the following. We sought to determine how long the influence of a past trial persists by using ambiguous motion quartets as stimuli. We found large, significant effects of all four most recent trials, but the results were not consistent with any priming model. The results could be explained instead as perceptual completion of two kinds of temporal patterns, repeating and alternating. We conclude that the visual system does not passively remember perceptual state: it analyzes recent perceptual history and attempts to predict what will come next. These predictions can alter what is seen.ambiguous figures ͉ apparent motion ͉ hysteresis ͉ priming V isual perception under ordinary circumstances is an ongoing process. Current visual information is integrated with past information as part of a perceptual cycle (1), and it is not surprising that, for example, the outcome of a given trial in a psychophysical experiment is affected by what has occurred in recent trials. The observer's response time on a particular trial, for example, is significantly affected by recent task history (2-8). This trial-to-trial effect of the past on the present is particularly pronounced in the perception of motion quartets, a commonly used apparent motion stimulus. A motion quartet consists of a brief display of two tokens presented at opposite ends of a diameter of an invisible circle followed a short time later by presentation of two other tokens on a possibly different diameter. With proper choice of timing, the observer sees apparent motion carrying one token of each pair to a token of the other (Fig. 1). The direction of perceived motion implies a correspondence between each token in the first pair and one of the tokens in the second. This pairing of tokens represents the visual system's solution to the motion correspondence problem (9 -11).The perceived motion is compelling, but it can also be ambiguous. When the tokens are all identical and the angle between the diameters is Ϸ90°, many observers are as likely to see movement in the clockwise direction as they are in the counterclockwise direction. By varying , the experimenter can vary the probability that the observer will perceive movement in one direction or the other. When is near 180°, motion is almost always seen as counterclockwise, and when it is near 0°, motion is almost always seen as clockwise.The perceived direction of motion is affected by proximity, the similarity between potentially corresponding tokens (9-14), and the direction of motion perceived during recent trials. Ramachandran and Anstis (15) found that the tendency for the observer to perceive the same direction of motion persisted even wit...

We examine the connection between a hypothetical kin recognition signal available in visual perception and the perceived facial similarity of children. One group of observers rated the facial similarity of pairs of children portrayed in photographs. Half of the pairs were siblings but the observers were not told this. A second group classified the pairs as siblings or nonsiblings. An optimal Bayesian classifier, given the similarity ratings of the first group, was as accurate in judging siblings as the second group. Mean rated similarity was also an accurate linear predictor (R2 = .96) of the log-odds that the rated pair portrayed were, in fact, siblings. Surprisingly, mean rated similarity did not vary with the age difference or gender difference of the pairs, both of which were counterbalanced across the stimuli. We conclude that the perceived facial similarity of children is little more than a graded kin recognition signal and that this kin recognition signal is effectively an estimate of the probability that two children are close genetic relatives.