Information-accumulation theory of speeded categorization.

A process model of perceptual categorization is presented, in which it is assumed that the earliest stages of categorization involve gradual accumulation of information about object features. The model provides a joint account of categorization choice proportions and response times by assuming that the probability that the information-accumulation process stops at a given time after stimulus presentation is a function of the stimulus information that has been acquired. The model provides an accurate account of categorization response times for integral-dimension stimuli and for separable-dimension stimuli, and it also explains effects of response deadlines and exemplar frequency.

A feature-sampling account of the time course of old-new recognition judgments.

This article describes the feature-sampling theory of recognition (FESTHER), a new model of the time course of recognition judgments based on a model of the time course of perceptual processing in categorization (K. Lamberts, 1995, 1998). FESTHER is applied to previous results and to data from 4 old-new recognition experiments. Experiments 1 and 2 provided a preliminary test of the model's ability to explain recognition judgments of simple objects under response deadlines. Experiments 3 and 4 involved a response-signal procedure to elicit recognition judgments at different time lags after presentation of a stimulus. Simple objects and words were used as stimuli in Experiments 3 and 4, respectively. The new model accounts well for the data from the 4 experiments and offers a parsimonious account of the time course of recognition judgments based on the time-dependent availability of stimulus information.

Basing categorization on individuals and events.

Exemplar, prototype, and connectionist models typically assume that events constitute the basic unit of learning and representation in categorization. In these models, each learning events updates a statistical representation of a category independently of other learning events. An implication is that events involving the same individual affect learning independently and are not integrated into a single structure that represents the individual in an internal model of the world. A series of experiments demonstrates that human subjects track individuals across events, establish representations of them, and use these representations in categorization. These findings are consistent with "representationalism," the view that an internal model of the world constitutes a physical level of representation in the brain, and that the brain does not simply capture the statistical properties of events in an undifferentiated dynamical system. Although categorization is an inherently statistical process that produces generalization, pattern completion, frequency effects, and adaptive learning, it is also an inherently representational process that establishes an internal model of the world. As a result, representational structures evolve in memory to track the histories of individuals, accumulate information about them, and simulate them in events.

Recognition times of different views of 56 depth-rotated objects: a note concerning Verfaillie and Boutsen (1995).

The present study examines the effect of the goodness of view on the minimal exposure time required to recognize depth-rotated objects. In a previous study, Verfaillie and Boutsen (1995) derived scales of goodness of view, using a new corpus of images of depth-rotated objects. In the present experiment, a subset of this corpus (five views of 56 objects) is used to determine the recognition exposure time for each view, by increasing exposure time across successive presentations until the object is recognized. The results indicate that, for two thirds of the objects, good views are recognized more frequently and have lower recognition exposure times than bad views.

First categorization of stimuli with multivalued dimensions.

The extended generalized context model's (EGCM's) ability to account for the time course of categorization of stimuli with multivalued dimensions was tested in two experiments. In each experiment, the participants were first trained to classify stimuli (semicircles of variable size with a radial line of variable orientation) into two categories. In the subsequent transfer stage, they categorized a set of transfer stimuli. The time available on each transfer trial was manipulated. Response had to be given within 400 msec, within 700 msec, or without time pressure. Different category structures were used in Experiments 1 and 2. The results of both experiments showed reliable effects of response deadline. The EGCM accounted for the data and performed consistently better than an alternative model.

Effects of multiple reference points in spatial stimulus-response compatibility.

In two experiments, spatial stimulus-response compatibility effects in situations where the stimulus could appear in eight different locations were investigated. The locations were obtained as a result of orthogonal manipulation of hemispace, visual hemifield within hemispace, and relative position within hemifield. In the first experiment, only relative position within hemifield was relevant for selecting one of two responses (left or right). The results showed that both hemifield and relative position formed the basis of compatibility effects. In the second experiment, which was in most respects identical to the first, all spatial information was irrelevant. Only the geometrical shape of the stimulus determined the correct response. The results showed three S-R compatibility effects, based on hemispace, hemifield, and relative position. These results contradict earlier findings, and have implications for models of stimulus-response compatibility.

Hemisphere-specific resource demands of task expectancies.

The hemisphere-specific resource demands of expecting letter- and figure-matching tasks were investigated, using dual-task methodology. Matching task expectancies were induced by blocking trials with respect to stimulus type (letters or geometrical figures). On one third of the trials, the matching stimuli were unexpectedly omitted. The secondary task required a speeded reaction to a laterally presented auditory probe. The side of probe presentation was unpredictable. Probe reaction times were taken as an index of the resource demands imposed by the primary task on the contralateral hemisphere. For both the trials with and without matching stimuli, probe reaction times showed a significant interaction between lateral side of probe presentation and block type (letters or figures). When letters were expected, reaction times were slower in the left-hemisphere probe task. Probe reaction times were equally fast for both sides when figures were expected. Overall, these results indicate that task expectancies primarily demand resources from the hemisphere that is specialized for carrying out the expected task.