We cordially invite you to the next
lecture of the BME Cognitive Seminar Series:
Location: BME, XI., Egry József utca 1., T. ép 515.
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/
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