Perceived duration,visual persistence, and neural integration

Abstract

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

Categorical and Prolonged Potentials Are Evoked when Brief, Intermediate-Intensity Flashes Stimulate Horseshoe Crab Lateral Eye Photoreceptors during Octopamine Neuromodulation

“…Moreover, the brief stimuli naturally associated with moving stimuli simply could not produce a sensory memory without some form of persistence. (In the psychophysical literature, such a persisting sensory memory has often been called an icon [46]. )…”

Dissociating sensory and cognitive contributions to visual persistence I. Photoreceptor response duration as a function of flash intensity, adaptation state, and candidate code

“…However, instead of simply producing a monotonic negative relationship between response duration and intensity, this candidate code also produced a nonmonotonic U-shaped relationship between these two variables. (In this context, it needs to be noted that the range of intensities which were used in both Nisly and Wasserman (1987) and in the present research was substantially greater than that used in most behavioral work. This leads to the expectation that using a behavioral task while covering a larger range than is typical in behavioral work might also produce a U-shaped curve.…”

“…We (Nisly and Wasserman 1987) previously presented what now seems to be a quite preliminary report of photoreceptor contributions. Our earlier experiments varied intensity and analyzed RPs using two dierent candidate sensory codes which were constructed to correspond to these narratives about the neural mechanisms underlying the two types of behavioral judgments.…”

“…Based on the work of Nisly and Wasserman (1987), it was expected that using a larger range of intensities than had typically been used in behavioral experiments might produce a Ushaped Drop Code function in both states of adaptation. Additionally, varying adaptation levels by two log units was expected to produce this U-shaped function in both the Full and Early Drop measures.…”

Receiver operating characteristic (ROC) analysis of neural code efficacies

“…Such considerations were extensively examined by Nisly and Wasserman (1987) and to a lesser degree by Felsten and Wasserman (1981). This reasonable question relates to the robustness of the present results, i.e., did the value of the criterion line affect the results?…”