Perceived duration,visual persistence,and neural integration

Varying stimulus intensity while measuring the perceived duration/visual persistence of brief light flashes has yielded disparate results. Some studies have found a direct relationship between the two variables; others have found an inverse relationship. Several models have been suggested to unify this behavioral literature. They invoke the absolute intensity and the nature of the judgment as explanatory variables. We now present physiological data whose analysis was motivated by these models. We measured the duration of photoreceptor potentials as a function of light intensity and response measure. One response measure was. the length of time required for the response to decline from the peak by a criterion amount. The other response measure was the length of time a response stayed above a criterion level. These data suggest that each behaviorally based model captured a different aspect of a single underlying mechanism and that a melding of the two critical concepts would harmonize all of the results: In this melding, the sensory signals that mediate visual perception would have the type of complex intensity- and time-dependent properties found in real neural responses.     

Intensity dependence of perceived duration: data, theories, and neural integration

Evaluates 2 theoretical models suggested to explain studies of the effect of stimulus intensity on the perceived duration of brief light flashes. Some studies found a direct relationship between the 2 variables; others found an indirect relationship. Each model suggests that an additional variable interacts with stimulus intensity. Proposed variables have included the nature of the judgment and the absolute intensity. The present evaluation indicates that both of the proposed variables play a role and that a melding of the models could best account for this phenomenon. The melding incorporates known time- and intensity-dependent characteristics of neural integration into the behavioral performance. The evaluation also indicates that future experiments on this problem will be most informative if they (a) give particular attention to the role of instructions, (b) explore an adequate range of intensities, and (c) strictly control adaptive state.     

Further remarks on the role of cognition in the comparative analysis of behavior

Recent interest in comparative psychology has stimulated much research and debate concerning cognitive processes in animal behavior. The present paper relates to this general area by treating particular issues in the analysis of comparative cognition: specifically, how cognition is inferred from animal behavior; whether the postulation of intervening cognitive processes furthers our understanding of behavior; and how rival approaches help advance the science of behavior.     

Stimulus selection with duration as a relevant cue

To date, research has not explicitly examined how duration competes with other stimulus dimensions for control over responding. The present study investigated some familiar selective mechanisms of stimulus control over key pecking in pigeons, with duration and line tilt as discriminative stimuli in successive discrimination procedures. Specifically, pigeon's key pecking was reinforced with food or extinguished following compound stimuli comprising one of two line orientation stimuli presented for one of two different durations. Traditional experimental designs explored stimulus additivity, overshadowing, blocking, and learned irrelevance. Although stimulus additivity was observed, control by duration was masked by line tilt in extinction testing that followed facilitated acquisition with redundant, relevant cues. In addition, although prior training with duration relevant partially blocked subsequent acquisition of control by line tilt when both stimulus dimensions were relevant, there was a tendency for control by duration to decrease with continued compound training. It was suggested that the greater time required to distinguish duration on a trial—compared to more commonly studied stimulus dimensions, which can be distinguished almost immediately—puts duration at a competitive disadvantage in situations where other relevant dimensions are also available.     

Backward Blocking and Recovery from Overshadowing in Human Causal Judgement: The Role of Within-compound Associations

We replicated and extended a project by Dickinson and Burke (1996) that concerned human causal judgement. In a medical diagnostic setting, college students' ratings of the causal efficacy of target cues showed retrospective revaluation: relative to a proper control condition, ratings of target cues both increased ('recovery from overshadowing') and decreased ('backward blocking') during a second stage of training in which competing cues, but not target cues, were presented. These changes in causal judgements were exhibited only by subjects who had learned which target and competing cues were paired with one another during the first stage of training. These results cannot be explained by the Rescorla-Wagner (1972) model of associative learning, but they can be explained by the revised model of Van Hamme and Wasserman (1994); the revised model assigns non-zero salience to nonpresented target stimuli whose memories or representations are retrieved by competing stimuli that had previously been paired with those target stimuli.     

Positive and negative patterning in human causal learning

Investigations of patterning discriminations by nonhuman animals have generally found that positive patterning is easier to learn than negative patterning. Studies of patterning discriminations in human causal learning tasks have failed to document any differences between positive and negative patterning. In the present study, human participants predicted an outcome on trials involving either a compound cue or its elements. Positive and negative patterning problems were successfully solved in a within-subjects design; negative patterning problems proved to be more difficult when an additional, 50% contingent cue was included (Experiment 2), but not when it was excluded (Experiment 1). Possible reasons for these results are discussed. The discussion concludes with an analysis of exemplar models (e.g., Pearce, 1994) of human causal learning and considers the conditions under which these models do and do not anticipate our results.     

Is Racial Profiling More Benign in Medicine Than Law Enforcement?

It might seem that racial profiling by doctors raised few of the same concerns as racial profiling by police, immigration, or airport security. This paper argues that the similarities are greater than first appear. The inappropriate use of racial generalizations by doctors may be as harmful and insulting as their use by law enforcement officials. Indeed, the former may be more problematic in compromising an ideal of individualized treatment that is more applicable to doctors than to police. Yet doctors, unlike police, should not attempt to ignore race altogether. Race and ethnicity are associated with the geography of disease, with social and cultural factors relevant to disease, and, to some extent, with genetic predispositions to disease. Moreover, greater attention to the distinctive health conditions of certain racial and ethnic groups is necessary to make up for past neglect. But it will be a tricky business to steer a middle course between a naïve, reckless, or dogmatic color blindness and a stereotype-driven overreliance on race and ethnicity. In trying to steer such a course, the doctor can only hope for the day when a combination of more individualized genomic medicine and greater social equality will make it possible for her to pay less attention to race and ethnicity without detriment to her patients?? health.     

Bayesian Model Selection and Model Averaging

This paper reviews the Bayesian approach to model selection and model averaging. In this review, I emphasize objective Bayesian methods based on noninformative priors. I will also discuss implementation details, approximations, and relationships to other methods. Copyright 2000 Academic Press.