MAGNETIC AND ELECTRICAL RESPONSES OF THE HUMAN BRAIN TO TEXTURE-DEFINED
FORM AND TO TEXTONS.
Regan, D., and P. He.
Institute For Space And Terrestrial Science and Departments of Psychology
and Biology, York University.
APStracts 2:0156N, 1995.
SUMMARY AND CONCLUSIONS
We searched for a neurophysical correlate of preattentive texture
discrimination by recording magnetic and electric evoked responses from the
human brain during the first few hundred msec following the presentation of
texture-defined (TD) checkerboard form. The only two textons that changed when
the TD checkerboard appeared or disappeared were the local orientation and
line termination textons. (Textons are conspicuous local features within a
texture pattern). Our evidence that the magnetic response to TD form cannot be
explained in terms of responses to the two associated textons is as follows:
(1) by dissociating the two responses we showed that the magnetic response to
TD form is almost entirely independent of the magnetic response to the local
orientation texton; (2) a further distinction between the two responses is
that their distributions over the head are different; (3) the magnetic
response to TD form differs from the magnetic response to the line termination
texton in both distribution over the head and waveform. We conclude that this
evidence identifies the existence of a brain response correlate of
preattentive texture discrimination. We also recorded brain responses to
luminance-defined (LD) checkerboard form. Our grounds for concluding that
magnetic brain responses to the onset of checkerboard form are generated by
different and independent neural systems for TD and LD form are as follows:
(1) Magnetic responses to the onset of TD form and LD form had different
distributions over the skull, had different waveforms and depended differently
on check size; (2) the waveform of the response to superimposed TD and LD
checks closely approximated the linear sum of responses to TD checks and LD
checks alone. One possible explanation for the observed differences between
the magnetic and electric evoked responses is that responses to both onset and
offset of TD form predominantly involve neurons aligned parallel to the skull,
while that is not the case for responses to LD form.
Received 19 September 1994; accepted in final form 17 April 1995.
APS Manuscript Number J586-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.