| |
Abstract:
Kanizsa-style illusory contours are perceived in the absence
of any "real" physical luminance gradients between inducers that
are spatially discontinuous. It has been controversial whether the
perception of these subjective contours arise from higher-level
cognitive mechanisms that depend on attention and serial search or
from lower-level parallel processing in the early automatic,
preattentive stages of vision. We studied the perception of Kanizsa
illusory figures in three patients who had unilateral spatial
neglect after a focal right hemisphere lesion. Even though neglect
patients were unable to detect the left-side inducers of Kanizsa
figures in a same/different judgment task, they were nonetheless
sensitive to the induced subjective contours in a midpoint judgment
task, so that they made identical bisection for figures with
illusory contours and figures with real contours but very different
bisection for other spatially discontinous figures that did not
yield illusory filling-in. Neglect patients can thus perceive the
subjective contours of an illusory figure without being aware of
left-side inducers. It is concluded that the grouping and
filling-in mechanisms that induce the illusory figure can occur
without explicit detection and conscious awareness of the inducing
features , consistently with the hypothesis that derive from
preattentive processes at earlier stages of vision.
|
