The phantom gap: an objective measure of para-saccadic masking M Duyck, T Collins, M Wexler |
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Laboratoire Psychologie de la Perception, CNRS & Université Paris Descartes, France
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| While we move our eyes under ordinary viewing conditions, we are not aware of the smears caused by the rapid visual motion on the retina during saccades. One explanation is that the smear is being masked by pre or post-saccadic static images. Evidence comes from subjective reports in experiments displaying a dot at different times around a saccade: if the dot is presented during the saccade only, observers perceive a phantom-like smear parallel to the saccade; but if it is also present before (forward mask) or after (backward mask) the saccade, shorter smears or single dots are perceived instead. We lit an LED during a saccade and inserted a brief luminosity decrement, resulting in the percept of an even more phantom-like gap inside the smear. By varying the time of the decrement we varied the position of the gap, which observers could reliably report using the method of single stimuli. We also varied the presence and duration of pre- and post-saccadic masks. Masks led to a large decrease in the slope of the psychometric function. This technique provides an objective measure of para-saccadic masking that may contribute to the study of its relation to classical or "fixational" masking. |
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