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Title: Use your illusion : the flash-lag effect as a tool for psychophysics
Author: Tilford, Robert Patrick
ISNI:       0000 0004 5365 7073
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2015
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The flash-lag effect is an illusion in which a moving object is perceived advanced beyond an aligned flash. The majority of research into the effect has been directed at specifying its source, though a small body of literature simply makes use of flash-lag to answer diverse questions about perception – without necessarily arbitrating between competing accounts of its nature. The current thesis expands on this little-explored potential of the flash-lag effect with the presentation of three papers reporting programmes of research that exploit the phenomenon to address issues unrelated to its cause. In the first paper it is shown that, like in visual flash-lag, a similar motion direction based anisotropy is evident in the motor version of the effect, in which one's unseen limb is perceived ahead of a flash. Specifically, the effect is greater for motion towards, rather than away from fixation. Furthermore, Paper I also demonstrates for the first time a motor flash-drag effect, in which one's unseen moving hand ‘drags' the perceived position of a nearby flash. It is argued that both of these findings are evidence of parallels between vision and action systems. Paper II takes advantage of the explicitly perceptual nature of the flash-lag effect to investigate whether the visuospatial perception of threatening objects is different to that of non-threatening objects. It is ultimately shown that when a moving stimulus is threatening, the flash-lag effect is greater, regardless of its direction of motion. Paper III shows that gamma movement (the apparent contraction of disappearing stimuli) adds to and subtracts from the forward displacement of contracting and expanding stimuli, respectively. Prior to these papers, however, an overview chapter reviews the flash-lag literature, and argues that the effect can be a useful tool for psychophysics, even without a consensus on its origin.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: BF0241 Special senses. Vision. Visual perception