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Lambon-Ralph, M. A., Hesketh, A., & Sage, K. (2004). Implicit recognition in
pure alexia: The Saffran effect - A tale of two systems or two procedures?
Cognitive Neuropsychology, 21, 401-421.
Notes: Prof. M.A. Lambon Ralph, Dept. of Psychology, University of
Manchester, Oxford Road, Manchester M13 9PL
Some patients with pure alexia or letter-by-letter reading demonstrate the
Saffran effect: residual activation of higher order lexical-semantic
representations despite poor word recognition. This study investigated the
reading of patient FD, a letter-by-letter reader with a clear Saffran effect.
Two alternative explanations for this effect were tested in a series of
experiments and through the impact of whole-word and letter-based therapies
on FD's reading. One theory assumes that the disparity between overt
recognition and implicit activation of word meaning is underpinned by two
separate reading systems. An alternative hypothesis argues for a single
whole-word reading system supplemented by the deliberate, compensatory
strategy of letter-by-letter reading. Under this hypothesis, the Saffran
effect reflects partial activation of the single, whole-word system. FD's
results strongly supported the latter hypothesis. FD's reading behaviour was
characterised by partial activation of higher word representations, accuracy
was graded by word variables known to influence the normal reading system,
and most importantly, once the characteristics of the tasks were equated,
there was no evidence for a dissociation between word categorisation and
recognition. In addition, the whole-word therapy encouraged FD to abandon
the letter-by-letter strategy. Without this compensatory technique, FD's
emergent deep dyslexia was consistent with a partially activated, whole-word
reading system that produces overt reading responses. Comparison of data
from this and other studies suggests that the Saffran effect is most likely
to be observed in patients with severe pure alexia.
Mechelli, A., Crinion, J. T., Long, S., Friston, K. J., Lambon-Ralph, M. A.,
Patterson, K. et al. (2005). Dissociating reading processes on the basis of
neuronal interactions. Journal of Cognitive Neuroscience, 17,
1753-1765.
Notes: Functional Imaging Laboratory, Wellcome Department of Imaging
Neuroscience, Institute of Neurology, London, UK. andream@fil.ion.ucl.ac.uk
Previous studies of patients with phonological and surface alexia have
demonstrated a double dissociation between the reading of pseudo words and
words with atypical spelling-to-sound relationships. A corresponding double
dissociation in the neuronal activation patterns for pseudo words and
exception words has not, however, been consistently demonstrated in normal
subjects. Motivated by the literature on acquired alexia, the present study
contrasted pseudo words to exception words and explored how neuronal
interactions within the reading system are influenced by word type.
Functional magnetic resonance imaging was used to measure neuronal responses
during reading in 22 healthy volunteers. The direct comparison of reading
pseudo words and exception words revealed a double dissociation within the
left frontal cortex. Pseudo words preferentially increased left dorsal
premotor activation, whereas exception words preferentially increased left
pars triangularis activation. Critically, these areas correspond to those
previously associated with phonological and semantic processing,
respectively. Word-type dependent interactions between brain areas were then
investigated using dynamic causal modeling. This revealed that increased
activation in the dorsal premotor cortex for pseudo words was associated
with a selective increase in effective connectivity from the posterior
fusiform gyrus. In contrast, increased activation in the pars triangularis
for exception words was associated with a selective increase in effective
connectivity from the anterior fusiform gyrus. The present investigation is
the first to identify distinct neuronal mechanisms for semantic and
phonological contributions to reading
20060321
Roberts, D. J., Lambon Ralph, M. A., & Woollams, A. M. (2010). When does
less yield more? The impact of severity upon implicit recognition in pure
alexia. Neuropsychologia, 48, 2437-2446.
Notes: Pure alexia (PA) is characterised by strong effects of word length on
reading times and is sometimes accompanied by an overt letter-by-letter (LBL)
reading strategy. Past studies have reported "implicit recognition" in some
individual PA patients. This is a striking finding because such patients are
able to perform semantic classification and lexical decision at above chance
levels even when the exposure duration is short enough to prevent explicit
identification. In an attempt to determine the prevalence of this "implicit
recognition" effect, we assessed semantic categorisation and lexical
decision performance using limited exposure durations in 10 PA cases. The
majority of the patients showed above chance accuracy in semantic
categorisation and lexical decision. Performance on the lexical decision
test was influenced by frequency and imageability. In addition, we found
that the extent to which patients showed evidence of "implicit recognition"
in both tasks was inversely related to the severity of their reading
disorder. This result is consistent with hypotheses which suggest that this
effect does not constitute an implicit form of unique word identification
but is a reflection of the degree of partial activation within the word
recognition system. These results also go some way towards explaining the
individual variation in the presence of this effect observed across previous
case-study investigations in the literature
Neuroscience and Aphasia Research Unit, School of Psychological Sciences,
University of Manchester, Manchester, UK
Roberts, D. J., Woollams, A. M., Kim, E., Beeson, P. M., Rapcsak, S. Z., &
Lambon Ralph, M. A. (2012). Efficient Visual Object and Word Recognition
Relies on High Spatial Frequency Coding in the Left Posterior Fusiform Gyrus:
Evidence from a Case-Series of Patients with Ventral Occipito-Temporal
Cortex Damage. Cerebral Cortex.
Notes: Recent visual neuroscience investigations suggest that ventral
occipito-temporal cortex is retinotopically organized, with high acuity
foveal input projecting primarily to the posterior fusiform gyrus (pFG),
making this region crucial for coding high spatial frequency information.
Because high spatial frequencies are critical for fine-grained visual
discrimination, we hypothesized that damage to the left pFG should have an
adverse effect not only on efficient reading, as observed in pure alexia,
but also on the processing of complex non-orthographic visual stimuli.
Consistent with this hypothesis, we obtained evidence that a large case
series (n = 20) of patients with lesions centered on left pFG: 1) Exhibited
reduced sensitivity to high spatial frequencies; 2) demonstrated prolonged
response latencies both in reading (pure alexia) and object naming; and 3)
were especially sensitive to visual complexity and similarity when
discriminating between novel visual patterns. These results suggest that the
patients' dual reading and non-orthographic recognition impairments have a
common underlying mechanism and reflect the loss of high spatial frequency
visual information normally coded in the left pFG
Neuroscience and Aphasia Research Unit, School of Psychological Sciences,
University of Manchester, Manchester, UK
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