Purchase this article with an account.
J.R. Pola; A Model of the Perceived Locations of Two Successively Flashed Targets during a Saccade . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1970.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: In a recent model, Pola & Wyatt (2002) suggested that when a single flashed target is presented during a saccade, its perceived location is due to the retinal (R) signal persistence of the flash interacting with a fast changing extraretinal (exR) signal. One consequence of this interaction, according to the model, is that the perceived location appears to arise from a slowly changing exR signal, in contrast to the actual fast exR signal. Other studies (Matin, Pola & Matin, 1972; Sogo & Osaka, 2002) show that when two successive flashes are presented, with a short inter-flash-interval, during a saccade, the perceived location of each flash is influenced by (i.e., is shifted toward) that of the other. The present study uses the model of Pola & Wyatt (2001) to explore the proposal (Matin, Pola & Matin, 1972) that the persistence of one flash together with the overlapping persistence of the other flash, are responsible for this mutual influence. Methods: In the model, the time interval between the two flashes varied from 0 to 300 ms. Each flash (5 ms) passed through a cascade of 1st order lags (time-constant = 15 ms) to give a R signal persistence of 250 ms. An exR signal was convolved with (a) the entire 1st-flash persistence and (b) that portion of the 2nd-flash persistence overlapping the 1st-flash persistence. The two resulting functions were combined to estimate the perceived location of the 1st-flash. A similar procedure was used to estimate the perceived location of the 2nd-flash. The two flashes (with a given inter-flash interval) were presented at 5 ms intervals, from before until after a saccade, to find the overall time course of perceived location. Results: With short inter-flash intervals (Δ t < 50 ms), and thus a large persistence overlap, the perceived location of each flash was influenced by the other flash. As the interval increased (50 ms < Δ t < 200 ms), the perceived location of each flash became increasingly similar to when the flash was presented alone. With large intervals (Δ t > 250 ms), and no persistence overlap, the perceived location was the same as when the flash was presented alone. Conclusions: The model’s "perceptual response" is quantitatively similar to the results of previous studies (Matin, Pola & Matin, 1972; Sogo & Osaka, 2002). Presumably, each flash, via persistence, is able to influence the other because the two flashes, seen together, are yoked by their relative retinal locations. Thus, persistence may be responsible, not only for the perception of single flashes and for an apparent slow exR signal, but also for perception in more complex situations, where two flashes or perhaps multiple stimuli are used.
This PDF is available to Subscribers Only