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Abstract:
Goal. In the "Thatcher illusion", a face in which the eyes
and mouth are inverted relative to the rest of the face, looks
grotesque when the face is shown upright but not when inverted. We
investigated the effects of this illusion in terms of global and
local processing of faces in normal observers, and in a visual
agnosic patient (HJA) who demonstrated prosopagnosia. Method.
Same-different matching experiments were conducted in which
observers judged whether pairs of faces were normal or
Thatcherized. HJA, a 79-year old male with bilateral
occipito-temporal lesions who showed visual agnosia and
prosopagnosia, was given similar tests. Results. Performance of
normal observers demonstrated a face inversion effect for normal
faces but not for Thatcherized faces, and for whole faces but not
for face parts. The absence of an inversion effect occurred when
the Thatcherized faces depicted the same or different individuals.
When the stimuli consisted of face parts only, no face inversion
effect occurred for normal or Thatcherized face parts. Patient HJA
performed at chance level for matching whole faces, but improved
considerably when matching face parts. Conclusion. Thatcherized
faces disrupt holistic processing of parts, thereby reducing any
advantage for upright faces. The prosopagnosic patient was
insensitive to the Thatcher illusion and processed face parts
better than whole face configurations.
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