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15 results

Space and Time in Perception and Action
  • Edited by Romi Nijhawan, Beena Khurana
  • Published online:
    05 October 2010
    Print publication:
    25 March 2010
  • What is the instantaneous position of a moving object from the point of view of the observer? How does a tennis player know when and where to place their racket in order to return a 120 mph serve? Does time stop sometimes and go faster at others? Space, time and motion have played a fundamental role in extending the foundations of 19th and 20th century physics. Key breakthroughs resulted from scientists who focused not just on measurements based on rulers and clocks, but also on the role of the observer. Research targeted on the observer's capabilities and limitations raises a promising new approach that is likely to forward our understanding of neuroscience and psychophysics. Space and Time in Perception and Action brings together theory and empirical findings from world-class experts and is written for advanced students and neuroscientists with a particular interest in the psychophysics of space, time and motion.

  • 27 - History and theory of flash-lag: past, present, and future

  • from Part IV - Spatial phenomena: forward shift effects
  • Edited by Romi Nijhawan, University of Sussex, Beena Khurana, University of Sussex
  • Book:
    Space and Time in Perception and Action
    Published online:
    05 October 2010
    Print publication:
    25 March 2010, pp 477-500

  • Summary

    Summary

    Some basic versions of the flash-lag effect have been known since the early decades of the twentieth century. Intriguingly, neural delays were as central in the early attempts at explaining the effect, as they are in the more recent investigations into its cause. For a changing visual stimulus a delayed registration of the stimulus by the central nervous system (CNS) constitutes an “error” between the instantaneously registered state of the stimulus on the one hand and its physical state on the other. Therefore, for animals to acquire food, mate, and avoid predators, compensation of sensory delays is essential. One may ask which component(s) of the CNS compensate for visual delays. Logically compensation could be carried out either by visual or motor mechanisms, or both. The motion extrapolation account of the flash-lag effect challenged the dominant view that only motor mechanisms compensate for visual delays, suggesting instead that visual mechanisms also contribute. Controversy fueled by empirical observations with unpredictable motion, in particular the flash-initiated and flashterminated conditions of the flash-lag effect, soon followed; prima facie motion extrapolation could not accommodate these results. Armed with these challenging findings (primarily) several alternative accounts of flash-lag were proposed. In light of new developments, this chapter evaluates the motion extrapolation, motion sampling, motion integration, postdiction, differential latency, and attentional cuing accounts of flash-lag.

  • 1 - Space and time: the fabric of thought and reality

  • Edited by Romi Nijhawan, University of Sussex, Beena Khurana, University of Sussex
  • Book:
    Space and Time in Perception and Action
    Published online:
    05 October 2010
    Print publication:
    25 March 2010, pp 1-6

  • Summary

    Space and time are modes by which we think and not the conditions in which we live.

    –Albert Einstein

    Since the beginning of sentience, the fabric of reality has been the subject of intense curiosity, and the twin concepts of space and time have figured prominently in the thinking of individuals of various intellectual persuasions. Understanding in science has advanced significantly through the postulates that underpin coherence and precision in the representation, and measurement, of space and time. These advances have formed the bedrock of the development of many disciplines. However, until the latter half of the nineteenth century many properties of space and time were assumed and therefore remained unquestioned. For example, the implicit acceptance of concepts such as absolute space (a coordinate system at rest, relative to which all inertial frames move at constant velocity) and absolute time (a universal time independent of any “clock” or mechanism) made most issues related to space and time impervious to empirical investigation and theoretical debate. This state of affairs was robustly challenged by scientists such as Ernst Mach, who among others imagined observers equipped with measuring devices (rulers and clocks) arriving at concepts at odds with notions of absolute space and absolute time.

    Many well-known scientists whose work spanned the latter half of the nineteenth century (Mach included) crossed the disciplinary boundaries of physics, philosophy, and vision science. In Mach's thinking on space and time, the observer's sense perception played a critical role.

  • What's in a name change? Visual prediction makes extrapolation real and functional

  • Beena Khurana
  • Journal:
    Behavioral and Brain Sciences / Volume 31 / Issue 2 / April 2008
    Published online by Cambridge University Press:
    14 May 2008, pp. 207-208

  • Nijhawan redraws our attention to the problem of accurately perceiving an ever-changing visual world via a sensory system that has finite and significant communication times. The quandary is compelling and stark, but the suggestion that the visual system can compensate for these transmission delays by extrapolating the present is not so unequivocal. However, in this current airing of contradictory issues, accounts, and findings, Nijhawan trades spatial extrapolation – a rather specific concept introduced earlier (in Nijhawan 1994) for visual prediction – a far more expansive notion that forces the issue of both the perceived reality and functional significance of compensation.