Functional neuroimaging of grammatical class: ambiguous and unambiguous nouns and verbs.

Neuropsychological and neuroimaging studies of grammatical-class differences suggest that nouns and verbs may be associated with different brain regions. The current functional magnetic resonance imaging (fMRI) study focused on auditory grammaticality judgements of two-word stimuli consisting of noun/verb ambiguous and unambiguous nouns and verbs preceded by either "the" or "to". The fMRI results showed effects of class ambiguity in the left inferior frontal gyrus, possibly due to greater selection demands, and effects of grammaticality ("yes" vs. "no" response) in left superior temporal gyrus, consistent with greater activation for trials with greater conflict. In addition, posterior left temporal lobe regions showed increased activity on unambiguous trials for verbs than for nouns, consistent with prior imaging studies. Thus, in a task specifically focused on the grammatical (rather than semantic) aspects of words and that used morphologically simple nouns and verbs controlled for imageability, verbs preferentially activated posterior temporal but not frontal lobe regions. However, for ambiguous trials in this same region, nouns showed greater activation than verbs, suggesting that these effects can be modulated by class ambiguity.

An investigation of attentional contributions to visual errors in right "neglect dyslexia".

One type of error that is sometimes produced by patients with acquired dyslexia is the substitution of an orthographically similar word with letters that overlap the target either in early or late letter positions. When such errors affect the left sides of words, they are usually produced by patients with focal right hemisphere lesions who typically show evidence of left neglect in non-reading tasks. This pattern has thus been termed "neglect dyslexia". When the right sides of words are affected, however, patients frequently fail to show any signs of neglect in tasks other than reading. This study presents results from a patient with left hemisphere damage, and a very clear pattern of right "neglect" errors in reading, on a series of tasks testing attentional and imagery processes. Given the magnitude and consistency of the patient's reading errors, there was little evidence that these errors resulted from inattention to the right side of space or to the right side of an internally generated visual image. It is argued that the positional errors result from an impairment to an abstract ordinal code with graded activation of letter positions from first to last, and that this code is specific to tasks involving orthographic representations.

Widening the temporal window: processing support in the treatment of aphasic language production.

Investigations of language processing in aphasia have increasingly implicated performance factors such as slowed activation and/or rapid decay of linguistic information. This approach is supported by studies utilizing a communication system (SentenceShaper) which functions as a "processing prosthesis." The system may reduce the impact of processing limitations by allowing repeated refreshing of working memory and by increasing the opportunity for aphasic subjects to monitor their own speech. Some aphasic subjects are able to produce markedly more structured speech on the system than they are able to produce spontaneously, and periods of largely independent home use of SentenceShaper have been linked to treatment effects, that is, to gains in speech produced without the use of the system. The purpose of the current study was to follow up on these studies with a new group of subjects. A second goal was to determine whether repeated, unassisted elicitations of the same narratives at baseline would give rise to practice effects, which could undermine claims for the efficacy of the system.

Orthographic effects in the word substitutions of aphasic patients: an epidemic of right neglect dyslexia?

Aphasic patients with reading impairments frequently substitute incorrect real words for target words when reading aloud. Many of these word substitutions have substantial orthographic overlap with their targets and are classified as "visual errors" (i.e., sharing 50% of targets' letters in the same relative position). Fifteen chronic aphasic patients read a battery of words and non-words; non-word reading was poor for all patients, and more than 50% of errors on words involved the substitution of a non-target word. An investigation of the factors conditioning these word substitutions, as well as the production of visual errors, identified a number of similarities to patterns previously reported for patients with right neglect dyslexia, which has been said to occur relatively rarely. These included a strong tendency for errors to overlap targets in initial letter positions, maintenance of target length in errors, and the substitution of words higher in imageability than targets. It is proposed that left hemisphere damage frequently leads to disruption of a level of representation for written words in which letter position is ordinally coded, resulting in exacerbation of a normal processing advantage for early letter positions. A computational model is discussed that incorporates this level of representation and successfully simulates relevant normal and patient data.

Comprehension of reversible sentences in aphasia: the effects of verb meaning.

Comprehension of semantically reversible active and passive voice sentences was tested in a timed sentence/picture verification task. Three sets of six verbs were identified that incorporated different features of meaning relevant to the assignment of nouns to the thematic role of agent. Normal control subjects showed an effect of verb set on their response times, with significant effects between sets in the predicted direction. A group of aphasic patients without sentence comprehension disorder also showed a significant effect of verb set despite long and variable response times. A group of patients with reversible comprehension disorder in screening tasks showed weaker effects, primarily because of the use of consistent response biases that ignored the sentence verb. An experimental treatment of active/passive comprehension was conducted with two of these latter patients; one patient reached ceiling in post-testing, and the other showed significant improvement but demonstrated residual comprehension problems that indicated differences across verb sets. Results support the critical importance of verb meaning to normal and aphasic sentence comprehension.