25 Oct
2012
25 Oct
'12
6:18 p.m.
We cordially invite you to the next lecture of the BME Cognitive Seminar
Series:
Date & Time: October 29, Monday, 12:00-13:00
Location: BME, XI., Egry József utca 1., T. ép 515.
*Sensory noise processing in the human brain: insights from object
recognition studies on healthy and amblyopic subjects*
*Bankó Éva*
Information Technology Department, Pázmány Péter Catholic University
Neurobionics Research Lab
http://vision.itk.ppke.hu/
Personal webpage: http://digitus.itk.ppke.hu/~banko/
<http://digitus.itk.ppke.hu/%7Ebanko/>
Abstract
Human visual object recognition is fast and efficient when viewing
conditions are good. However, under low visibility conditions the visual
system must recruit additional processing resources to handle the noisy
and deteriorated visual images, thus object recognition becomes more
effortful. Even though this is often the case, little is known about the
neural mechanisms engaged in processing of noisy images. This is even
more important since adding noise to images is widely used in
decision-making studies to modulate task difficulty while not taking
into account the confound introduced by the increased sensory processing
demands. In a series of experiments on healthy and amblyopic subjects we
have pinned down both in time and space the active processes associated
with sensory noise processing using faces with decreased
phase-coherence. Namely, phase noise affects the electrophysiological
responses in the first 300 ms following stimulus onset that is unrelated
to changes in task-difficulty; most importantly, there is an increase in
the ERP single-trial (i.e. true) response amplitudes between 200 - 300
ms after stimulus onset -- involving the P2 component -- the
noise-modulation of which is diminished in amblyopia. This amblyopic
deficit measured on the P2 component predicted the severity of the
noise-related behavioral impairments and could not be explained by an
overall increase in stimulus uncertainty or task difficulty in the case
of noisy stimuli, which have been also proposed previously as
explanations of the noise-related ERP changes. On the other hand, the
noise-modulation of the N170 component of the ERP responses --
reflecting structural processing of face images -- was similarly
affected by the presence of noise in the amblyopic and the fellow eye of
amblyopes, suggesting that the noise-induced decrease of the N170 could
simply be due to the decrease in the face content of the images.
Furthermore, we also showed that processing of phase randomized as
compared to intact faces is associated with increased fMRI responses in
specific areas of the lateral occipital cortex. These results suggest
that efficient processing of noisy images depends on the engagement of
visual cortical mechanisms that take place after the early structural
processing of visual objects has been completed and is reflected in the
P2 component of the ERP response sand most likely localized to a
retinotopic part of the lateral occipital cortex that has been
implicated in grouping and image segmentation.
--
Attila Keresztes
Junior Research Fellow
Budapest University of Technology and Economics
Dept. of Cognitive Science,
Egry József u. 1, Budapest
1111, Hungary
Tel: +36 1 4633525