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.

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 ofthe 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 oftime 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.Visual sensations need not last for the same amount of time as the light flashes that evoke them. If, as is often the case, the sensation outlasts the stimulus, then one can talk about visual persistence: the length of time between the end of the stimulus and the end of the sensation. Alternatively, one can talk about perceived duration; it is usually operationally defined as the time from stimulus onset to the end of the sensation. Sometimes, however, perceived duration is defined as the interval between the beginning and end of the sensation. Whichever measure is used, differences between objective and subjective duration are particularly interesting for two reasons: First, they are quite obviously expressions of the mechanisms that create subjective representations of the external world. Second, they also provide particularly tractable material for quantitative empirical investigation. A large number of studies have therefore measured the effects of stimulus intensity on visual persistence and perceived duration; the results of these studies have not been uniform. Some of these studies have found a direct relationship, whereas other studies have found an inverse relationship.Several hypotheses have been offered to explain these variant results (see

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