Extrapolation or attention shift?

Khurana, Beena; Nijhawan, Romi

doi:10.1038/378566a0

Cited by 106 publications

(109 citation statements)

References 8 publications

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“…It is known that the flash-initiated flash-lag condition, in which the moving object abruptly starts at the same time as the flash is shown, leads to an unabated flash-lag effect (Khurana & Nijhawan, 1995). In other words, an abrupt onset does not lead to a reduction in error or a more accurate localization, as we propose the offset does here.…”

Section: Discussionmentioning

confidence: 62%

Going, going, gone: Localizing abrupt offsets of moving objects.

Maus¹,

Nijhawan²

2009

Journal of Experimental Psychology: Human Perception and Perfor

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When a moving object abruptly disappears, this profoundly influences its localization by the visual system. In Experiment 1, 2 aligned objects moved across the screen, and 1 of them abruptly disappeared. Observers reported seeing the objects misaligned at the time of the offset, with the continuing object leading. Experiment 2 showed that the perceived forward displacement of the moving object depended on speed and that offsets were localized accurately. Two competing representations of position for moving objects are proposed: 1 based on a spatially extrapolated internal model, and the other based on transient signals elicited by sudden changes in the object trajectory that can correct the forward-shifted position. Experiment 3 measured forward displacements for moving objects that disappeared only for a short time or abruptly reduced contrast by various amounts. Manipulating the relative strength of the 2 position representations in this way resulted in intermediate positions being perceived, with weaker motion signals or stronger transients leading to less forward displacement. This 2-process mechanism is advantageous because it uses available information about object position to maximally reduce spatiotemporal localization errors.Keywords: flash-lag effect, backward masking, visual transients, motion extrapolation, moving objects Supplemental materials: http://dx.doi.org/10.1037/a0012317.suppIn the flash-lag effect, a moving object appears to be ahead of a spatially aligned flashed object. This finding has sparked a debate about how the nervous system processes moving objects and determines their perceived position. This is an important problem as neural delays in the retina and the central vision pathway are liable to lead to spatial localization errors. One hypothesis, termed motion extrapolation, states that moving objects are spatially shifted forward to counteract the influence of neural delays in the visual pathways on the perceived position of moving objects (Nijhawan, 1994). If one assumes that perceptual awareness of the position of an object requires cortical activity, then a delay in the pathway from the photoreceptors to the primary visual cortex of about 80 ms (Schmolesky et al, 1998) would imply that moving objects are always perceived to lag their "true" position by the distance they moved in that time. However, by analyzing the speed and direction of a moving object, the visual system could extrapolate its position forward by an appropriate amount and so compensate for these processing delays. In the flash-lag effect, this forward shift is apparent, because the flash does not undergo an equivalent spatial shift, thereby resulting in a perceived gap between the moving object and the flash, although they are physically aligned.Several alternative accounts have been brought forward to explain the findings of the flash-lag effect, amongst them differential attentional deployment

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Section: Discussionmentioning

confidence: 62%

Going, going, gone: Localizing abrupt offsets of moving objects.

Maus¹,

Nijhawan²

2009

Journal of Experimental Psychology: Human Perception and Perfor

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“…Under the same conditions, the visuomotor error was 1.188 (1.03 cm), which would compensate for a temporal delay of 95 ms. Some studies have suggested that the visual system corrects for transmission delays using operations akin to extrapolation, whereby the perceived position of a moving object is extrapolated forwards in time based on its speed, trajectory and neural latency (Nijhawan 1994;Khurana & Nijhawan 1995;Sheth et al 2000). The extrapolation hypothesis was based on studies of the`£ash-lag phenomenon', in which a continuously moving bar is perceived to be ahead of a stationary £ashed (stroboscopically illuminated) bar when the two images are spatially aligned on the retina.…”

Section: Discussionmentioning

confidence: 99%

Evidence for dissociation between the perceptual and visuomotor systems in humans

Yamagishi

Anderson

Ashida

2001

Proc. R. Soc. Lond. B

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When a visual stimulus is continuously moved behind a small stationary window, the window appears displaced in the direction of motion of the stimulus. In this study we showed that the magnitude of this illusion is dependent on (i) whether a perceptual or visuomotor task is used for judging the location of the window, (ii) the directional signature of the stimulus, and (iii) whether or not there is a signi¢cant delay between the end of the visual presentation and the initiation of the localization measure. Our stimulus was a drifting sinusoidal grating windowed in space by a stationary, two-dimensional, Gaussian envelope ( 1 cycle of sinusoid). Localization measures were made following either a short (200 ms) or long (4.2 s) post-stimulus delay. The visuomotor localization error was up to three times greater than the perceptual error for a short delay. However, the visuomotor and perceptual localization measures were similar for a long delay. Our results provide evidence in support of the hypothesis that separate cortical pathways exist for visual perception and visually guided action and that delayed actions rely on stored perceptual information.

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“…Thus the illusory line-motion results from a gradient of attentional facilitation that radiates in all directions from the cued location and weakens with distance (LaBerge 1983;LaBerge and Brown 1989;McCormick and Klein 1990;Stelmach and Herdman 1991;Stelmach et al 1994;Schmidt et al 1998;but see Downing and Treisman 1997). Khurana and Nijhawan (1995) tested such an attentional account by exploring both the spatial and temporal delays posited by the`attention shift' hypothesis. They presented observers with a display in which flashed and moving elements were spatially interleaved.…”

Section: Attentional Accountmentioning

confidence: 99%

“…An`early' visual operation, computationally akin to extrapolation, has been suggested to correct the cortical lag and maintain position correspondence between different processing levels for predictably moving objects (Nijhawan 1994(Nijhawan , 1997Khurana and Nijhawan 1995;Nijhawan and Khurana, in press). Consequently, the retinotopic site in the cortex maximally activated by a moving object will be the same as that activated by a stationary object located where the moving object is at any given instant in time.…”

Section: Introductionmentioning

confidence: 99%

“…3 Two accounts of the flash-lag effect Multiple accounts of the flash-lag effect have been forwarded, such as visible persistence (Mach 1897;Nijhawan 1992;Krekelberg and Lappe 2000), informational content (MacKay 1958), motion extrapolation and delay (Nijhawan 1994(Nijhawan , 1997Khurana and Nijhawan 1995;Nijhawan and Khurana, in press), attentional delay (Baldo and Klein 1995), differential visual latencies (Purushothaman et al 1998;Whitney and Murakami 1998;Whitney et al 2000), and most recently, postdiction (Eagleman and Sejnowski 2000). We shall outline the extrapolation-and-delay account and the attentional account in detail to provide the motivation behind the present experiments and reserve discussion of the other accounts until after the presentation of the results.…”

Section: Introductionmentioning

confidence: 99%

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The Role of Attention in Motion Extrapolation: Are Moving Objects ‘Corrected’ or Flashed Objects Attentionally Delayed?

2000

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Objects flashed in alignment with moving objects appear to lag behind [Nijhawan, 1994 Nature (London) 370 256–257], Could this ‘flash-lag’ effect be due to attentional delays in bringing flashed items to perceptual awareness [Titchener, 1908/1973 Lectures on the Elementary Psychology of Feeling and Attention first published 1908 (New York: Macmillan); reprinted 1973 (New York: Arno Press)]? We overtly manipulated attentional allocation in three experiments to address the following questions: Is the flash-lag effect affected when attention is (a) focused on a single event in the presence of multiple events, (b) distributed over multiple events, and (c) diverted from the flashed object? To address the first two questions, five rings, moving along a circular path, were presented while observers attentively tracked one or multiple rings under four conditions: the ring in which the disk was flashed was (i) known or (ii) unknown (randomly selected from the set of five); location of the flashed disk was (i) known or (ii) unknown (randomly selected from ten locations), The third question was investigated by using two moving objects in a cost – benefit cueing paradigm, An arrow cued, with 70% or 80% validity, the position of the flashed object, Observers performed two tasks: (a) reacted as quickly as possible to flash onset; (b) reported the flash-lag effect, We obtained a significant and unaltered flash-lag effect under all the attentional conditions we employed, Furthermore, though reaction times were significantly shorter for validly cued flashes, the flash-lag effect remained uninfluenced by cue validity, indicating that quicker responses to validly cued locations may be due to the shortening of post-perceptual delays in motor responses rather than the perceptual facilitation, We conclude that the computations that give rise to the flash-lag effect are independent of attentional deployment.

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Extrapolation or attention shift?

Cited by 106 publications

References 8 publications

Going, going, gone: Localizing abrupt offsets of moving objects.

Going, going, gone: Localizing abrupt offsets of moving objects.

Evidence for dissociation between the perceptual and visuomotor systems in humans

The Role of Attention in Motion Extrapolation: Are Moving Objects ‘Corrected’ or Flashed Objects Attentionally Delayed?

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