The Flash-lag Effect And Its Cognitive Mechanism

In the visual environment, some objects are invariant and some change in a continuous fashion. The human visual system is known to judge relative spatial position with high accuracy and precision, even when stimuli are moving at considerable speed on the retina.Surprisingly, however, there is the growing evidence that the perceived position of an object is influenced by the object's motion. For example, when a flashed object is spatially aligned with a moving object, observers tend to indicate that the position of the flashed object lags behind that of the moving object. The amount of lag has often been quantified as the flash's nulling position, which is the physical spatial offset needed to establish perceptual alignment. This phenomenon has been referred to as the flash-lag effect.Over the last few decades, there have been several hypotheses put forth to explain the flash-lag effect: differential persistence, motion extrapolation, differential latency, temporal integration and postdiction.In summary, different accounts of the flash-lag effect fall into two categories on the basis of their assumptions. Accounts in one category invoke previously un-established neural processes underlying motion. Both extrapolation (latency-correction) and differential latency (latency-reduction) models invoke the biological significance of detecting a moving object quickly and its position accurately, and the ensuing increased likelihood of successful interceptive behavior. The flash, on this view, is simply a spatiotemporal marker with no special properties other than those already known (neural delay and visual persistence). Accounts in the second category invoke previously un-established neural processes underlying flashes. The postdiction model assumes that the flash resets with ongoing motion integration.However, recent psychophysical experiments suggest that neither of these interpretations is feasible.A reason for the debate over the cognitive mechanism of the flash-lag effect is that the researcher neglected to regard the temporal processing and spatial processing of the stimulus in this effect as a whole. The competing accounts have been proposed invoke only one side of processes and the question of initial coding and storage of stimuli has been largely bypassed.It is well known that the perceptual experience of a briefly presented visual stimulus persists beyond the physical stimulus itself. This persistence is called visual sensory memory (VSM). It is characterized as a high-capacity, transient visual icon. Information in the sensory memory is un-interpreted. But there has been rarely known about the auto-process of the sensory representation in the visual sensory memory.Here, we associate the visual sensory memory with one elementary perceived attribute——brightness. Temporal factor affect brightness perception via visual sensory memory. And brightness of an object also depends on its spatial context. Therefore, the representation of the spatio-temporal information is a indivisible entity.In the past decade, there has been a great deal of experimental research on the factors for influence the flash-lag effect. Some factors have been proposed in the previous studies, for example, the speed of the moving stimulus, the relative luminance between flash and moving stimulus, the spatial predictability of the flash and the retinal eccentricity of the flash. Most researchers emphasized on these effects from a spatial analytic perspective instead of temporal perspective.To avoid the shortages of former studies,this article introduce the connection between the visual sensory memory and the brightness of stimulus to the research of the flash-lag effect., and separate this effect into components, reduce and induce the elementary factors for influence that effect. Then we suggest an innovative cognitive mechanism underlying the flash-lag effect. In this dissertation:1.On the basis of characteristic of the sensory storage, by presenting an adjoining stimulus transiently, we show that the moving objects are still represented at their veridical positions in the flash-lag effect. There is no spatial offset between the sensory signals of the moving object and flash in early visual areas.2.Using idea of reduction and induction, we analyze the flash and motion of the moving object in that effect,then discuss their spatio-temporal characteristic. We compare the flash-lag effect with another similar illusion——Fr?hlich effect, in which a rapidly moving object coming out from an occluding edge was seen to appear not at the edge, but only at some distance from the edge in the direction of motion. We investigate the effect of attention and metacontrast masking on the sensory representations of the moving object during motion. 3.We first take the idea of auto-process in the visual sensory memory as a tool to research the flash-lag effect, and introduce brightness of stimuli changes over time due to this auto-process. Therefore we manipulate the contrast polarity of the flash to validate the role of the visual sensory memory in the flash-lag effect.4.A new concept of"instantaneous mutual contrast"is introduced. Similar to the simultaneous contrast effect, the brightness of an object which present transiently also depends on its spatial context. The higher the surrounding brightness is, the lower sensitivity of sensory representation of the briefly presented target stimulus becomes. The observed result will be affected by the fuzzy perception attributable to the instantaneous mutual contrast.5.Develop an innovative cognitive mechanism underlying the flash-lag effect on the basis of the above experiments and analyses.