Visual processing in Autism-spectrum disorders

People with autism and related disorders (Autism spectrum disorders; ASD) are
generally thought of as having difficulties in the domain of social
interactions. However, increasing amount of evidence is suggesting that people
with ASD also have atypical perceptual and cognitive styles. For example,
people with ASD have a tendency to focus on details, rather than a big picture.
Recent evidence suggests that the underlying cause of this preference for
details is not related to cognitive style, but rather stems from a
pre-attentive increase in perceptual saliency. In other words, people with ASD
don't choose to pay attention to detail; they see the details as more distinct
and therefore as more noticeable. This apparent distinctness of the details, in
turn, is more likely to capture their attention. It is possible that a child
who perceives the world in such an atypical way is likely to develop an
atypical interaction with the world it is growing up in. Since social
interactions are particularly important for us, the atypical interactions with
the world that the child is growing up in are likely to be particularly
pronounced in the social domain. It is, therefore, of paramount importance to
determine why this atypical perceptual function arises.

The question of interest is why this is the case. One possibility is that the
atypically high perceptual salience of details for people with ASD is a
consequence of atypical neuronal responsiveness to visual stimulation. Since at
the neural level the pop-out effect has related to a phenomenon called surround
suppression. Surround suppression refers to a neural mechanism by which
activity of a visually-responsive neuron is reduced through inhibitory
interconnections with neurons that code for space surrounding the receptive
field of that particular neuron if the visually responsive neurons are
sensitive to the same type of information (e.g. vertical orientations). The
pop-out occurs when surround suppression results in lower activity levels for
neurons responding to the homogeneous background, while no such suppression
acts upon the neurons that respond to the distinctive target.

It is also of interest to examine whether atypical neuronal responsiveness to
visual stimulation is restricted to the first stage of cortical visual
processing, or whether this effect is present at multiple levels of visual
processing hierarchy. If the differences between people with and without ASD
are restricted to a single level of visual processing hierarchy, then the
atypical perceptual experience may reflect a single, modality-specific,
mechanism. Alternatively, if the effects are present at multiple visual areas,
then the atypical perceptual experience may reflect a more general
over-activation of inhibitory connections. To resolve that possibility, we aim
to develop visual stimuli that are optimized for the hierarchically
lowest-level visual areas: V1/V2 and V3.

In order to determine whether the difference in inhibition effects between
people with and without ASD is related to differences in perceptual
sensitivity, we plan to also compare the two groups on a behavioural task
testing for perceptual sensitivity.

The main objective of the current study is to examine whether people with ASD
have over-active inhibitory inter-connections in visual processing areas that
can account for their over-sensitivity to perceptual dissimilarities.

We propose a between-group experimental study. We will use fMRI and EEG to
determine whether people with ASD show greater degree of cortical inhibition in
response to homogeneous displays than inhomogeneous displays. The displays will
be designed in such a way so that they match the receptive-field properties of
cortical neurons in areas V1/V2 and V3. We will use a behavioural task to
determine whether people with ASD show greater degree of reduction of
perceptual sensitivity associated with greater degree of cortical inhibition.
The design of the study will follow a 2x2x2 design with display type
(homogeneous or inhomogeneous) and stimulus type (optimised for V1/V2 or V3) as
within-group factors, and ASD-diagnosis as a between-group factor.

The participation will involve 3 separate sessions: one for fMRI and
behavioural testing (up to 2 hours), one for EEG, behavioural and IQ testing
(up to 2.5 hours). An additional diagnostic session will be required for some
participants, in case additional diagnostic tests need to be administered (up
to an hour). Therefore, the participants will be required to come to the site 2
times in order to complete both sessions. Participants will be compensated for
their time with a payment of 10 euro per hour, which should add up to 50 euro
if the participants complete the entire study.

There are no foreseeable risks involved associated with the behavioural and IQ
testing. Functional MRI measurements are considered to be invasive and there
may be incidental findings of pre-existing brain abnormalities.