How do we prioritize what we see?
New research uncovers the causal role of the occipital cortex

Date:
August 13, 2020
Source:
New York University
Summary:
It is known that different regions of the brain help us
prioritize information so we can efficiently process visual
scenes. Neuroscientists have discovered that one specific region,
the occipital cortex, plays a causal role in piloting our attention
to manage the intake of images.



FULL STORY ==========================================================================
It is known that different regions of the brain help us prioritize
information so we can efficiently process visual scenes. A new study
by a team of neuroscientists has discovered that one specific region,
the occipital cortex, plays a causal role in piloting our attention to
manage the intake of images.


==========================================================================
The work, which appears in the latest issue of the journal Current
Biology, relies on a method, transcranial magnetic stimulation (TMS),
which helps illuminate this dynamic.

"By briefly disrupting cortical excitability of the occipital cortex with
TMS we could extinguish the known effects of involuntary, or exogenous,
covert spatial attention, and thus reveal a causal link between the
occipital cortex and the effect of covert attention on vision," explains
Marisa Carrasco, a professor of psychology and neural science at New
York University and the senior author of the paper.

"This is a surprising finding as most previous research shows that other
areas of the brain -- the frontal and parietal cortex -- help us in
selectively processing many images that come our way, but this research
reveals that the occipital cortex also plays a critical functional role,"
adds Antonio Ferna'ndez, an NYU doctoral student and first author of
the paper.

In our daily lives, we are bombarded with an overwhelming amount of
sensory information, notably visuals, from as big as skyscrapers to as
small as computer screens. In spite of this, we have the impression of effortlessly understanding what we see, unaware of the complex mechanisms
that, in a kind of cognitive triage, help us prioritize the information
that we process. It's been long shown that the processing of visual
information and its accompanying neural computations consume a great
deal of energy, which is finite and must be managed.

One of the ways we achieve this is through covert spatial attention,
which enables us to select a certain location of a visual scene and
prioritize its processing and guide behavior, even without moving our
eyes to that location (which is why it is called covert).



========================================================================== Covert attention, whether voluntary (endogenous) or involuntary
(exogenous), is a trade-off process -- it benefits visual processing at
the attended location at the expense of processing elsewhere.

Earlier neuroimaging and electrophysiological studies have shown that
visual areas in the occipital cortex, located in the back of the brain,
are part of the attention cortical networks, but it was unknown whether
this region is necessary in the prioritizing of visual content.

Because of its well-established role in vision, Ferna'ndez and Carrasco specifically sought to determine if the occipital cortex played a causal
role in guiding involuntary (exogenous) covert attention.

To do so, they conducted a series of experiments with human observers
and used TMS to manipulate and briefly alter cortical excitability in
the occipital area.

The authors asked the participants to make an orientation judgement
by determining if an image was tilted right or left on a computer
screen. They also manipulated participants' covert attention with an
additional image -- a cue (small line) that appeared on the screen
prior to stimuli presentation to automatically attract attention to its location. One stimulus appeared left and the other stimulus appeared
right off center, while observers fixated at a central point. The
cortical representation of one of the two stimuli was briefly disrupted
using TMS. In some trials, "valid trials," the cue indicated the stimulus location observers should respond to; in other trials, "invalid trials,"
the peripheral cue indicated the other stimulus location. In neutral
trials, both stimuli were cued.

This design allowed the investigators to record responses at the
attended and unattended locations with and without stimulation. Without
TMS, behavioral responses reflected the typical performance benefits
(valid trials compared to neutral trials) and costs (invalid trials
compared to neutral trials) at attended and unattended locations,
respectively. However, with TMS disrupting activity in the occipital
cortex, the responses were the same regardless of the nature of the
attentional cue, and both behavioral benefits and costs were eliminated.

The research was supported by grants from the National Institutes of
Health (R21-EY026185, T32 EY007136-27).


========================================================================== Story Source: Materials provided by New_York_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Antonio Ferna'ndez, Marisa Carrasco. Extinguishing Exogenous
Attention
via Transcranial Magnetic Stimulation. Current Biology, 2020;
DOI: 10.1016/j.cub.2020.07.068 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200813123558.htm

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