Gist-based illusions within and across stimulus modalities in autism spectrum disorder.

Some studies have reported a low rate of false recognition (FR) in individuals with autism spectrum disorder (ASD) relative to non-autistic comparison participants (CPs). This finding, however, has not always been replicated and the source of the discrepancy remains unknown. We hypothesised that poor episodic memory functions may account for this finding. We used an adapted version of the Deese, Roediger and McDermott paradigm which presents lists of words, pictures or word-picture pairs to obtain measures of performance which reflect episodic [hits and false alarms (FAs)] and semantic (FR) memory functions. Results showed a decreased rate of FR in ASD individuals with lists of words which rose above the rate seen in non-autistic CPs with lists of word-picture pairs. This increased rate of FR in ASD was accompanied by a parallel increase in hits and a decrease in FA which reached a similar level in the two groups. Poor episodic memory functions may prevent individuals with ASD from acquiring item information which in turn precludes the formation of semantic links between items. This could render them less prone to FR.

Pantomimes are special gestures which rely on working memory.

The case of a patient is reported who presented consistently with overt deficits in producing pantomimes in the absence of any other deficits in producing meaningful gestures. This pattern of spared and impaired abilities is difficult to reconcile with the current layout of cognitive models for praxis. This patient also showed clear impairment in a dual-task paradigm, a test taxing the co-ordination aspect of working memory, though performed normally in a series of other neuropsychological measures assessing language, visuo-spatial functions, reasoning function, and executive function. A specific working memory impairment associated with a deficit of pantomiming in the absence of any other disorders in the production of meaningful gestures suggested a way to modify the model to account for the data. Pantomimes are a particular category of gestures, meaningful, yet novel. We posit that by their very nature they call for the intervention of a mechanism to integrate and synthesise perceptual inputs together with information made available from the action semantics (knowledge about objects and functions) and the output lexicon (stored procedural programmes). This processing stage conceived as a temporary workspace where gesture information is actively manipulated, would generate new motor programmes to carry out pantomimes. The model of gesture production is refined to include this workspace.

Naming rotated pictures and the riddle of object-centred neglect.

In this study eight patients with left neglect were asked to name chimerical pictures of objects and animals with different spatial orientation: standard upright position, rotated 180 degrees, rotated 90 degrees to the right, and rotated 90 degrees to the left. All patients showed the typical pattern of egocentric neglect. They omitted the left part of the normally upright pictures and the right part of the inverted stimuli, now falling in the left space. When the pictures were tilted 90 degrees to the right, they reported the two component objects with the same level of accuracy. However, at variance with egocentric neglect, when the chimerical pictures were rotated 90 degrees to the left, the patients omitted the left half of the stimulus more often than the right half. We propose that since in the latter condition the less informative lower part of the pictures was available in the non-neglected space, the patients mentally rotated the perceived stimulus and aligned it with its upright orientation before naming its component parts. In our interpretation, the mental orientation and normalisation of rotated stimuli might underlie all the reported evidence of object-centred neglect for non-orthographic stimuli.

Afferent dysgraphia after right cerebral stroke: an autonomous syndrome?

Afferent dysgraphia is an acquired writing deficit characterized by deletions and duplications of letters and strokes. The commonly accepted interpretation states that afferent dysgraphia is associated with three main clinical features: production of spatial writing errors; the presence of left unilateral neglect; and no deterioration in performance when writing blindfolded. In order to test whether these symptoms necessarily co-occur with afferent dysgraphia, we studied the writing performances of a series of eight right brain-damaged patients. In sentence copying, spontaneous handwriting, and writing to dictation they showed afferent dysgraphia. However, signs of left neglect and spatial dysgraphia were evident only in some cases. Furthermore, the frequency of afferent errors increased when patients were required to write without vision. The present study demonstrates that afferent dysgraphia is an autonomous clinical entity and that it results from a selective impairment of a mechanism whose function is that of comparing the information about the number of letters and strokes specified at the level of letter motor programs and the actual number of movements already realized.

Cognition in action: testing a model of limb apraxia.

Assessment of limb apraxia is still suffering from Liepmann's legacy and performance in gesture-processing tests is generally rendered by classifying patients' profile according to the classic clinical labels of ideomotor and ideational apraxia. At odds with other cognitive functions, interpretation of apraxia has suffered from a lack of a reliable model which does justice to its complexity. Recently such a model has been proposed (Rothi et al., 1991, 1997). In this article a modified version of this model is presented and predictions are made according to its functional architecture. Five different patterns of impairment of gesture processing are postulated. To validate the predicted performance profiles, 19 left-hemisphere-damaged patients were assessed by means of an ad hoc battery of four praxis tests. Four of the five predicted apraxia patterns were observed, the fifth being more equivocal. These results support the need to overcome the simplistic dichotomous view of apraxia and confirm the fruitfulness of a model of normal gesture processing in order to understand dissociations in apraxia.

Neglect without extinction.

A patient, AB, is reported who showed clear signs of neglect but no extinction (N+ E-). Several hypotheses proposed to account for this dissociation were put to the test. The postulated association between motor neglect and extinction did not hold good, nor did the possibility that the N+ E- dissociation may be traced back to the difference in test requirements and therefore observed only in patients with object-centred neglect. Likewise, manipulating the physical features of the stimuli (relative size, exposure time, presentation synchrony) did not elicit extinction. However, when the task demands were modified by asking the patient to perform a further spatial analysis of the stimuli, rather than simply detect them, extinction emerged. Since AB performed well on several neglect tasks requiring parallel processing, while failing all tasks calling for serial processing, the hypothesis is put forward that AB's N+ E- dissociation could be interpreted within the parallel/serial distinction framework.

Dissociation between recency and span: neuropsychological and experimental evidence.

This article reports dissociations between verbal span and the recency portion of the serial position curve in immediate free recall, in 2 neuropsychological case studies and in 3 experiments with normal participants. Patient A. N. presented with an impaired serial verbal span while showing an intact recency effect. The opposite pattern was observed in patient G. C., who despite a poor recency showed normal span in verbal serial recall tasks. Experiments 1 and 2 showed a recency effect with visually and auditory presented lists and written recall was resistant to the effects of articulatory suppression and of irrelevant speech, but was disrupted by the suffix effect. Experiment 3 showed that in contrast with recency, memory span was affected by articulatory suppression and irrelevant speech during presentation but not by a suffix. These findings are not consistent with the idea that span and recency measure aspects of the same memory system. Moreover, in clinical practice, they should not be used as equivalent alternatives.

Left of what? The role of egocentric coordinates in neglect.

OBJECTIVES: Egocentric coordinate systems centred on the trunk, head, and gaze have been investigated in a patient who displays severe extrapersonal neglect and in five control subjects. METHODS: The subjects were tested with a blind tactile exploration task in five different experimental conditions in which the role of the three distinct frames of reference was individually controlled. RESULTS: Only the trunk centred coordinates significantly influenced the performance of the patient, therefore proving of paramount importance in determining the boundaries of the neglected field. Similar results emerged from a single word reading task, in which the patient's performance improved when the stimuli were presented to the right of his body's midline. CONCLUSION: These findings point to the importance of the body centred coordinate system in determining the area of extrapersonal spatial neglect.

Dissociation between word reading and word copying in a patient with left visual neglect.

A patient with left visual neglect following a right hemisphere infarction is described. When presented with isolated words and nonwords, she made left neglect errors in reading aloud, but not in direct copying. This finding suggests a distinction between two ways of processing orthographic stimuli: depending on the task, the unit of processing can be the letter string or the single letter. In reading, the letter string is treated as a whole while in copying it is processed element-by-element. Left neglect differentially affects the processing of single words: in reading errors involve the left, initial letters, while in copying they involve the single letters, or the left part of the letters, independently of their position within the stimulus.

Ignoring left and far: an investigation of tactile neglect.

The aims of this paper were to identify patients with tactile neglect, to corroborate its independence from visual neglect, to ascertain its presence along the radial dimension of space and to detect a gradient of performance, as recently reported for visual neglect. To this end eight patients with vascular right cerebral lesions and 28 healthy controls have been tested with a modified version of the tactile maze test of De Renzi et al. [Cortex, vol. 6, pp. 191-203, 1970] and a seven-test clinical battery to detect the presence of visual USN. Four patients presenting tactile USN were selected: two showed left tactile neglect while the other two showed tactile neglect for far space. The distribution of omissions showed a clear spatial gradient. Since our patients were blindfolded, neglect behaviour in the tactile domain cannot be attributed to the attractive power of visual information. However, 25% of the normal subjects were also significantly faster in the 'near' space pointing towards the possibility that neglect for 'far' space can reflect the exaggeration of a normal asymmetry.

The effect of space location on neglect depends on the nature of the task.

It has been often reported that in patients with visual neglect line bisection is more accurate in the right than in the left hemispace. However, no data are available on the effect of hemispace on reading errors associated with neglect. We examined a 62-year-old man who presented with severe left neglect following a large infarction in the right cerebral hemisphere. The patient was asked to read 180 words aloud and to bisect 90 lines. Stimuli were presented in three different spatial locations: across the centre, to the right or to the left of the body midline. Line bisection was significantly more accurate in the right hemispace compared with the centre, or the left hemispace. In contrast, reading was significantly more accurate with words presented on the left side than on the centre or right side. This is the first time that such dissociation has been reported. We hypothesize that the dissociation depends on the nature of the stimuli and on the different cognitive demands of the tasks.

A reappraisal of the controversy of Dax and Broca.

Paul Broca is unanimously recognized as the founder of neuropsychology. Helis development of the scientific method to map mental functions onto brain topographpy has been enormously influential. Nevertheless, Dax's paper on the left hemisphere dominance for speech was written and published before Broca explicitely proposed the same theory. Probably, Broca was aware of the paper prior to 1865, but he never acknowledged Dax's original theoretical contribution. On the contrary, he always claimed to be the first to espouse the theory of left hemisphere dominance for language and never quoted Marc Dax (Broca, 1877 p 536), 'I do not like dealing with the questions of priority concerning myself. That is the reason why I did not mention the name of Dax in my paper'. In our opinion, the weight of evidence reported here suggests that the theory of the left hemisphere dominance for speech must be attributed equally to Dax and Broca, and henceforth should be called 'the theory of Dax-Broca'.

Perseverative dysgraphia: a selective disorder in writing double letters.

Models of writing processes postulate that abstract graphemic representations contain information about letter doubling independent of letter identity. We describe a patient, R.T., who made perseverative errors only in handwriting geminate letters, [e.g.: "CORTECCIA" (cortex)-->"CORTECCCIA"]. Perseveration was specific to orthography. To explain R.T.'s errors, we argue that after the selection of the correct graphic motor programs, the geminate feature induced a perseverative graphic behaviour. This form of dysgraphia supports the notion that graphemic representations contain specific information about letter doubling.

Anarthria impairs subvocal counting.

We studied subvocal counting in two pure anarthric patients. Analysis showed that they performed definitively worse than normal subjects free to articulate subvocally and their scores were in the lower bounds of the performances of subjects suppressing articulation. These results suggest that subvocal counting is impaired after anarthria.

Implicit associative priming in a patient with left visual neglect.

Recent studies have suggested that patients with visual neglect may process, even if without awareness, perceptual features of the neglected stimuli. The aim of the current study was to further investigate whether the ignored stimuli are processed at a deeper level. Findings from a patient with damage to the right hemisphere and with left visual neglect (no hemianopia) are reported. He showed an associative priming in the neglected space: response to a word in the right visual field was faster when the word was preceded by the brief presentation of an associated word in the neglected field. When obliged to orient attention to the left side of a computer screen, he was not able to detect the presence of, to read aloud, or to judge the lexical status and semantic content of left-sided stimuli. This patient was able to perform a covert post-perceptual processing of the neglected stimuli, but could not do so when explicitly requested.

Horizontal and vertical neglect dyslexia.

This case study concerns a 25-year-old right-handed male patient (G.G.) with post-traumatic lesions involving the right temporal and occipital lobe as well as the basal forebrain of the same side. G.G., who had a visual field defect almost limited to the upper left quadrant, showed both left horizontal and lower vertical neglect dyslexia, disproportionately severe when compared with left and lower visuo-spatial neglect. This is the first case report of a patient whose neglect dyslexia for vertical stimuli depended upon stimulus orientation, i.e., errors affected the final letters of top-down words and the initial letters of the bottom-up ones. This implies that neglect dyslexia can affect the internal letter shape map not only along the horizontal, but also along the vertical axis.

Inner speech in anarthria: neuropsychological evidence of differential effects of cerebral lesions on subvocal articulation.

The role of articulation in verbal short-term memory was investigated in two anarthric patients, C.M. and F.C., both showing normal comprehension for written and spoken language, above average intelligence and visuo-spatial abilities. Based on experimental results, we propose that subvocal articulation might be impaired in anarthric patients in different ways, according to the site of lesion: in 'locked-in' patients only the articulatory rehearsal processes necessary to enhance memory performances is involved, while in cortical anarthric patients the lesion affects the articulatory recoding processes involved in transferring visually presented material into an articulatory form for better retention.

A selective deficit for writing vowels in acquired dysgraphia.

Brain-damaged patients with acquired writing disorders provide important information about the normal processes of spelling and writing. Current models indicate that to produce a letter string, its 'abstract' representation is computed and stored in a temporary orthographic buffer, from which it is converted to a verbal code (if the word is to be spelled aloud) or to a physical letter code (if the word is to be written). The stored graphemic representations specify the identity and order of the component letters and their consonant/vowel status. Here I describe the spelling performance of two patients with a selective deficit in writing vowels. When writing words, the first patient omitted all vowels, leaving a blank space between consonants or consonant clusters, whereas the second produced errors that almost exclusively involved vowels. This pattern of performance supports the hypothesis that the consonant/vowel status of graphemes is differentially specified in the spelling process and may be selectively affected after brain damage.