Use your illusion: the flash-lag effect as a tool for psychophysics

Tilford, Robert Patrick (2015) Use your illusion: the flash-lag effect as a tool for psychophysics. Doctoral thesis (PhD), University of Sussex.

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Abstract

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.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Psychology > Psychology
Subjects: B Philosophy. Psychology. Religion > BF Psychology > BF0231 Sensation. Aesthesiology > BF0241 Special senses. Vision. Visual perception
Depositing User: Library Cataloguing
Date Deposited: 09 Jun 2015 15:33
Last Modified: 28 Sep 2015 15:19
URI: http://sro.sussex.ac.uk/id/eprint/54345

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