Article,
Language-specific tuning of visual cortex? Functional properties of the Visual Word Form Area.
Brain, (2002)
Abstract
The first steps in the process of reading a printed word belong to
the domain of visual object perception. They culminate in a representation
of letter strings as an ordered set of abstract letter identities,
a representation known as the Visual Word Form (VWF). Brain lesions
in patients with pure alexia and functional imaging data suggest
that the VWF is subtended by a restricted patch of left-hemispheric
fusiform cortex, which is reproducibly activated during reading.
In order to determine whether the operation of this Visual Word Form
Area (VWFA) depends exclusively on the visual features of stimuli,
or is influenced by language-dependent parameters, brain activations
induced by words, consonant strings and chequerboards were compared
in normal subjects using functional MRI (fMRI). Stimuli were presented
in the left or right visual hemifield. The VWFA was identified in
both a blocked-design experiment and an event-related experiment
as a left-hemispheric inferotemporal area showing a stronger activation
to alphabetic strings than to chequerboards, and invariant for the
spatial location of stimuli. In both experiments, stronger activations
of the VWFA to words than to strings of consonants were observed.
Considering that the VWFA is equally activated by real words and
by readable pseudowords, this result demonstrates that the VWFA is
initially plastic and becomes attuned to the orthographic regularities
that constrain letter combination during the acquisition of literacy.
Additionally, the use of split-field stimulation shed some light
on the cerebral bases of the classical right visual field (RVF) advantage
in reading. A left occipital extrastriate area was found to be activated
by RVF letter strings more than by chequerboards, while no symmetrical
region was observed in the right hemisphere. Moreover, activations
in the precuneus and the left thalamus were observed when subjects
were reading RVF versus left visual field (LVF) words, and are likely
to reflect the attentional component of the RVF advantage.
Tags
- adult;
- comparative
- cortex;
- evoked
- female;
- gov't;
- humans;
- imaging;
- language;
- magnetic
- male;
- non-u.s.
- nonparametric;
- pattern
- perception
- photic
- potentials;
- reading;
- recognition,
- research
- resonance
- statistics,
- stimulation;
- study;
- support,
- visual
- visual;
