Visual processes in a hemialexic patient with posterior callosal section

A patient with surgical section of the splenium and, probably, the posterior end of the truncus of the corpus callosum was studied 9-13 yr after the operation. His reading aloud, reading comprehension and word-matching abilities were moderately disturbed only in the left hemifield. These three disturbances were equally disturbed. The disturbances were not the result of visual disturbances such as tachistoscopic hemiamblyopia or tachistoscopic hemineglect since Landolt's ring matching was intact in the left hemifield as well as in the right. The disturbances were also not due to the disturbance of tachistoscopic word perception since the patient correctly performed same-different judgment of pairs of words in each hemifield. In his reading aloud and reading comprehension disturbances, ideogram words were less impaired than phonogram words, even when the number of letters in the words was the same. His picture naming ability was not disturbed in each hemifield.     

Transcortical sensory aphasia: Dissociation between naming and comprehension

Abstract

Although anomia in transcortical sensory aphasia (TSA) is usually described as a semantically based deficit (naming and recognition are equally affected), dissociations in naming performance have occasionally been reported. We report a two-part study: in Study 1 the pattern of preserved and impaired language abilities was examined in five patients with TSA and intact object naming; in Study 2 the neural mechanism(s) underlying preserved visual confrontation naming in TSA was examined. Demographic factors, severity of language deficits, lesion volume and location, and cerebral asymmetries of patients with TSA and intact naming (TSA-intact) (n = 6) were compared with those of patients with TSA and impaired naming (TSA-impaired) (n = 6), anomic aphasia (Anomia) (n = 6), and left hemisphere damage without aphasia (Control). The results of Study 1 revealed that all five patients had a relative preservation of oral production (spontaneous speech, repetition, naming and reading aloud), but impaired auditory and written (sentence-level) comprehension. Object/picture naming was significantly better than auditory comprehension of the same targets, and naming was also preserved in tactile and auditory (verbal definitions and non-verbal sounds) modalites, but written naming was impaired. In four patients oral reading showed a pattern of phonological dyslexia. The results of Study 2 failed to demonstrate significant differences between the groups with preserved naming (TSA-intact and control) and those with impaired naming (TSA-impaired and anomia) in non-language variables that might explain the selective preservation or impairment of naming. These results are discussed in terms of the functional and anatomical independence of the neural systems responsible for object naming and comprehension.     

Temporal segregation deficit in visual perception: A single case study

Abstract

The patient (LD) presents a visual deficit In temporal segregation. PET scan showed a bilateral hypometabolism in the superior parietal, temporal and occipital cortex. Neuropsychological data revealed that memory, attention and language functions were almost completely preserved. Visual sensory tests showed that visual acuity, depth and colour perception were normal, whereas detection of apparent motion direction, flicker fusion and saccadic eye movements were abnormal. Shape drawing was impaired whereas shape recognition (and naming), with either static or dynamic stimuli, was good. LD failed in tasks requiring Integration of elements to produce a whole image (line drawings, degraded and textured shapes). On the other hand, LD's performance was good in tasks not involving spatial integration, such as visual search and letter-by-letter reading. The main finding is that LD failed in tasks requiring temporal segregation. These tasks involved shape recognition when different shapes (Experiment la) or different parts of either a word or a shape presented successively on the same retinal locus with (Experiments 2b, 3a, 3b) and without (Experiments 4a, 4b) eye movements. Finally, LD has no problems in tasks (4c) involving temporal integration alone. Taken together, these results suggest damage to a general mechanism involved in temporal segregation.     

Visual hemisfield effects in dichoptic presentation of digits.

A visual analogy to dichotic listening was used in order to test hemispheric asymmetry in perception of verbal stimuli. Tachistoscopic perception of rival digits presented dichoptically was compared in the two visual hemifields. Directional scanning tendencies were controlled by using Ss with opposing reading habits. The results pointed at the interaction of right visual field superiority in perception with the effect of directional scanning, therefore suggesting that both mechanisms influence the perceptual asymmetry for verbal material. A subsidiary finding was superior perception of the noncrossed retinal inputs as compared with crossed retinal inputs, observed in two experiments one involving unilateral and the other bilateral presentation to both visual fields.     

Tactile agnosia and tactile aphasia: symptomatological and anatomical differences.

Two patients with tactile naming disorders are reported. Case 1 (right hand tactile agnosia due to bilateral cerebral infarction) differentiated tactile qualities of objects normally, but could neither name nor categorize the objects. Case 2 (bilateral tactile aphasia after operation of an epidural left parietal haematoma) had as severe a tactile naming disturbance as Case 1, but could categorize objects normally, demonstrating that tactile recognition was preserved. Case 1 may be the first case of tactile agnosia clearly differentiated from tactile aphasia. CT scans of Case 1 revealed lesions in the left angular gyrus, and in the right parietal, temporal, and occipital lobes. Case 2 had lesions in the left angular gyrus and of posterior callosal radiations. Our findings suggest that tactile agnosia appears when the somatosensory association cortex is disconnected by a subcortical lesion of the angular gyrus from the semantic memory store located in the inferior temporal lobe, while tactile aphasia represents a tactual-verbal disconnection.     

Preserved ability to read aloud kanji idioms in left handed alexia]

We report a 69-year-old left-handed man, who developed alexia after a right medial occipito-temporal lobe infarction. On admission to the rehabilitation department two months after the onset, neurological examination showed left hemianopia, left hemiparesis, decreased deep sensation on the left side, and alexia. A brain MRI demonstrated infarcts in the right medial occipito-temporal lobe and the splenium of the corpus callosum. Detailed neuropsychological examination was performed two months after the onset. The patient was alert and cooperative. His speech was fluent with some word-finding difficulty. Comprehension for spoken materials, repetition, and naming abilities were all preserved. Systematic examination for reading revealed that reading aloud was disturbed in both kanji and kana words. Reading comprehension was significantly better for kanji words than kana words. First, we examined the effects of number of characters in a word. The number of characters in a word didn't affect his reading performance. Second, his performance on reading aloud of usual kanji words was compared with that of kanji words representing idioms. A kanji idiom is different from usual kanji words, in which pronunciation of each character is selected from several options. Reading aloud kanji idioms was significantly better than usual kanji words. In addition, reaction time to complete reading a word was much shorter for kanji idioms than usual kanji. An analysis of qualitative features of errors revealed that most errors in kanji idiom reading were semantically similar to the correct answers, while many errors in usual kanji word reading were classified into "don't know" responses. These findings suggested that a kanji idiom was tightly connected to its pronunciation, which resulted in his much better performance for kanji idiom reading. Overlearning of a unique relationship between a kanji idiom and its pronunciation might modify neuronal organization for reading.     

Cerebral networks for number processing: Evidence from a case of posterior callosal lesion

Abstract

We report a study of number processing in a patient with a lesion selectively destroying the posterior half of her corpus callosum. This case provided an opportunity to study the cerebral distribution of numerical abilities across hemispheres, and their interhemispheric communication pathways. Tasks of interhemispheric same-different judgement with digits and sets of dots showed that exact digit identity could not be transferred between hemispheres, but that some approximate magnitude information could. With arabic numerals presented in the left visual field, reading aloud and arithmetic were severely impaired. In contrast, larger-smaller magnitude comparison was spared. With right-visual-field stimuli, the patient's performance was essentially normal in reading aloud, arithmetic and number comparison. These findings lend support to the hypothesis that both hemispheres are capable of identifying arabic digits, and of accessing and comparing the corresponding magnitudes. However, the verbal abilities which underlie overt naming and arithmetic computations are available only to the left hemisphere.     

Anomic alexia of kanji in a patient with anomic aphasia

The ability to read aloud kanji (logogram) words and to comprehend their meaning was systematically examined to clarify the underlying mechanism of kanji alexia in a patient with anomic aphasia. Confrontation naming, reading aloud and reading comprehension tasks were performed using 110 words from 11 semantic categories written in kanji or kana. Performance in oral reading of kanji words was significantly worse than oral reading of the same words transcribed into kana words. In addition, for kanji words reading aloud was much worse than reading comprehension. Oral reading of kanji words had a significant correlation with naming pictures corresponding to the words, but no correlation with comprehension of kanji words. Qualitative analyses demonstrated that errors in oral reading and naming tasks had many features in common. Our results indicated that some common mechanisms underlie both naming and oral reading of kanji words. We propose calling this type of alexia "anomic alexia of kanji", which should be distinguished from kanji alexia with difficulty in both reading aloud and comprehension. Lesions in our patient were located in the middle part of the left middle temporal gyrus and its subcortical area, which could be important for access to the phonological lexicon from semantics.     

Colour anomia restricted to the left visual hemifield after splenial disconnexion.

In a patient with damage to the right occipital lobe and to the splenium of the corpus callosum, an incomplete colour anopia in the left upper quadrants and a colour anomia was found for the complete left visual hemifield beyond 2 degrees eccentricity. The patient had no difficulty in recognising coloured targets when presented in the periphery of the left visual hemifield and in the foveal region, but could not name them correctly. The results suggest that the lesion of the splenium of the corpus callosum disconnects the right visual cortex from the language areas of the left hemisphere, and the specific disturbance of colour naming is the consequence.     

Reading aloud in jargonaphasia: an unusual dissociation in speech output.

A patient is described who showed several dissociations between oral and written language processing after bilateral retrorolandic vascular lesion. Dissociation was firstly between abolished auditory comprehension and preserved written comprehension and then involved confrontation naming, clearly superior in the written modality. The third striking dissociation involved oral output; spontaneous speech, although fluent and well articulated, consisted of neologistic jargon, while reading aloud was clearly superior though not perfect. Data are discussed with reference to a cognitive model of word processing. The pattern of dissociation in word production may be due to a failure in retrieving the phonological word form from the semantic system.     

Matching is not naming: A direct comparison of lexical manipulations in explicit and implicit reading tasks

The neurobiological basis of reading is of considerable interest, yet analyzing data from subjects reading words aloud during functional MRI data collection can be difficult. Therefore, many investigators use surrogate tasks such as visual matching or rhyme matching to eliminate the need for spoken output. Use of these tasks has been justified by the presumption of “automatic activation” of reading‐related neural processing when a word is viewed. We have tested the efficacy of using a nonreading task for studying “reading effects” by directly comparing blood oxygen level dependent (BOLD) activity in subjects performing a visual matching task and an item naming task on words, pseudowords (meaningless but legal letter combinations), and nonwords (meaningless and illegal letter combinations). When compared directly, there is significantly more activity during the naming task in “reading‐related” regions such as the inferior frontal gyrus (IFG) and supramarginal gyrus. More importantly, there are differing effects of lexicality in the tasks. A whole‐brain task (matching vs. naming) by string type (word vs. pseudoword vs. nonword) by BOLD timecourse analysis identifies regions showing this three‐way interaction, including the left IFG and left angular gyrus (AG). In the majority of the identified regions (including the left IFG and left AG), there is a string type × timecourse interaction in the naming but not the matching task. These results argue that the processing performed in specific regions is contingent on task, even in reading‐related regions and is thus nonautomatic. Such differences should be taken into consideration when designing studies intended to investigate reading. Hum Brain Mapp 34:2425–2438, 2013. © 2012 Wiley Periodicals, Inc.     

Left neglect dyslexia and the effect of stimulus duration

The present study investigated the effects of the duration of the stimulus on the reading performance of right-brain-damaged patients with left neglect dyslexia. Three Italian patients read aloud words and nonwords, under conditions of unlimited time of stimulus exposure and of timed presentation. In the untimed condition, the majority of the patients' errors involved the left side of the letter string (i.e., neglect dyslexia errors). Conversely, in the timed condition, although the overall level of performance decreased, errors were more evenly distributed across the whole letter string (i.e., visual - nonlateralized - errors). This reduction of neglect errors with a reduced time of presentation of the stimulus may reflect the read out of elements of the letter string from a preserved visual storage component, such as iconic memory. Conversely, a time-unlimited presentation of the stimulus may bring about the rightward bias that characterizes the performance of neglect patients, possibly by a capture of the patients' attention by the final (rightward) letters of the string.     

Two systems for colour-naming defects: verbal disconnection vs colour imagery disorder

Two subjects affected by pure alexia and showing no central dyschromatopsia or generalized aphasia, performed poorly on traditional tasks with visually-presented colour stimuli and on tasks with objects presented verbally. Three experiments were conducted to evaluate the possible role of mental colour imagery in recalling the colours of objects from memory. It was concluded that Case I, with left occipital lobe softening, had preserved imagery systems, but failed to recode the colours of mentally generated colour images, just as he failed to name visually presented colours, suggesting a language-imagery disconnection. In contrast, Case II, with a bilateral occipital lesion, had sustained damage to her long-term visual memories for colours as chromatic attributes of objects. This content-specific imagery deficit was concomitant with colour agnosia. The present findings are discussed in terms of current cognitive theories on imagery deficits.     

Visual word form processing in the right hemisphere: Evidence from neuropsychological investigations in two Chinese patients with a splenium lesion

Background: Though there is no doubt that the left hemisphere (LH) is the superior language processor, an increasing number of researches have demonstrated significant linguistic ability in the “nonverbal” right hemisphere (RH), such as orthographic processing and the superiority of recognising words presented in unfamiliar formats. However, it is difficult to rule out the role of the LH in language processing completely, because the subjects reported in most studies have no lesion or commissurotomy in the splenium of the corpus callosum (SCC), which allowed the interaction between left and right hemispheres in visual word processing. Patients with a lesion or commissurotomy in the SCC provide a unique opportunity to explore visual word form processing in the RH.

Aims: The study involved a series of neuropsychological tests to investigate visual word form processing in the RH.

Methods & Procedures: Two unique Chinese patients with a splenium lesion were asked to complete a series of neuropsychological tests, consisting of the Line Bisection Test, Albert Cancellation Test, the Aphasia Battery of Chinese (ABC), mini-mental state examination (MMSE) and visual word form processing (reading aloud, lexical decision in the Song typeface and handwritten styles) presented tachistoscopically in left or right visual field.

Outcomes & Results: We found that two patients had difficulties in reading simple and compound Chinese characters presented tachistoscopically in the left visual field (LVF), called left hemialexia, while their lexical decision-making ability in the LVF was relatively spared. In addition, the two patients’ performance on lexical decision-making in the LVF declined to a random level in the handwritten styles.

Conclusions: These findings provide direct supporting evidence that the RH is important for processing a character’s orthographic form and suggest that the LH is necessary for extracting an abstract presentation of a character in visual word form processing.     

Kinesthetic alexia due to left parietal lobe lesions

To investigate the neuropsychological mechanisms of kinesthetic alexia, we asked 7 patients who showed kinesthetic alexia with preserved visual reading after damage to the left parietal region to perform tasks consisting of kinesthetic written reproduction (writing down the same letter as the kinesthetic stimulus), kinesthetic reading aloud, visual written reproduction (copying letters), and visual reading aloud of hiragana (Japanese phonograms). We compared the performance in these tasks and the lesion sites in each patient. The results suggested that deficits in any one of the following functions might cause kinesthetic alexia: (1) the retrieval of kinesthetic images (motor engrams) of characters from kinesthetic stimuli, (2) kinesthetic images themselves, (3) access to cross-modal association from kinesthetic images, and (4) cross-modal association itself (retrieval of auditory and visual images from kinesthetic images of characters). Each of these factors seemed to be related to different lesion sites in the left parietal lobe.     

Repetitive transcranial magnetic stimulation of the dominant hemisphere can disrupt visual naming in temporal lobe epilepsy patients.

We used repetitive transcranial magnetic stimulation (rTMS) to study visual naming in 14 patients with temporal lobe epilepsy. Ten had left hemisphere language by Wada testing and all experienced speech arrest with rTMS of the motor speech area in the left frontal lobe. One left-hander had speech arrest with stimulation of sites on both sides. Subjects were asked to name pictures or read words presented on a computer monitor. rTMS was delivered on half of the trials. Stimulation sites were the motor speech area in the left frontal lobe, the mirror site on the right, and the left and right mid superior and posterior temporal lobes. rTMS at left hemisphere sites caused more naming errors than did right hemisphere rTMS. All individual subjects, except two who had temporal lobe resections and the one with bilateral speech arrest, produced more naming errors with rTMS of left hemisphere sites. There was no significant effect on word reading. rTMS at the left hemisphere and right frontal sites produced reductions in reaction time for picture naming, but not for word reading. This was observed for both correct and incorrect responses. This study shows that left hemisphere rTMS can disrupt visual naming selectively.     

How do patients with neglect see a horizontal line?

Abstract. Twelve patients with left unilateral spatial neglect were examined with a newly devised coloured line bisection task. They were presented with a horizontal line printed in blue on one side and in red on the other side; the proportions of the blue and red segments were varied. Immediately after placement of the subjective midpoint, the line was concealed and the patients were asked to name the colours of the right and left ends. Five patients who identified the left-end colour almost correctly had no visual field defect, while the other seven whose colour naming was impaired on the left side had left visual field defect. The rightward bisection errors were similarly distributed in the fair and poor colour-naming patients except for two patients from the latter group. The lesions of the fair colour-naming patients spared the lingual and fusiform gyri, which are known to be engaged in colour processing. Patients with neglect whose visual field is preserved may neglect the leftward extension of a line but not the colour in the neglected space. The poor colournaming patients frequently failed to name the left-end colour that appeared to the left of their subjective midpoint, which indicates that they hardly searched leftward beyond that point. In such trials, they reported that the left end had the same colour as the right end. The results suggest that in patients with neglect and left visual field defect, both the leftward extent and the colour of a line may be represented on the basis of the information from the attended right segment.     

Progressive Anomia with Preserved Oral Spelling and Automatic Speech

We report a patient, Newton, with a progressive classical anomia resulting from focal degeneration of the left hemisphere. In naming tasks Newton spelt aloud picture names that he could not retrieve, indicating a dissociation between orthography and phonology. Unusually, his writing and letter-pointing performance were impaired and spelling was achieved only through alphabet recitation. A study of automatic speech tasks demonstrated strikingly preserved naming performance on automatic compared to nominative tasks. We argue that automatic tasks provide phonological cues that facilitate phonological activation. With progression of disease Newton has shown increasing difficulty reading and repeating words, which we interpret in terms of a progressive elevation in the threshold for activation of phonology. Phonological cueing of picture names has yielded superior naming than word reading and even repetition, a finding consistent with the notion that task characteristics influence likelihood of phonological activation and naming success, but contrary to the notion that there exist separate task-specific output systems. We conclude that Newton exhibits a unique pattern of deficits, which have theoretical relevance for the debate on the relationship between phonology and orthography, the role of automatic speech and the relationship between naming, reading and repetition.     

Progressive anomia with preserved oral spelling and automatic speech

We report a patient, Newton, with a progressive classical anomia resulting from focal degeneration of the left hemisphere. In naming tasks Newton spelt aloud picture names that he could not retrieve, indicating a dissociation between orthography and phonology. Unusually, his writing and letter-pointing performance were impaired and spelling was achieved only through alphabet recitation. A study of automatic speech tasks demonstrated strikingly preserved naming performance on automatic compared to nominative tasks. We argue that automatic tasks provide phonological cues that facilitate phonological activation. With progression of disease Newton has shown increasing difficulty reading and repeating words, which we interpret in terms of a progressive elevation in the threshold for activation of phonology. Phonological cueing of picture names has yielded superior naming than word reading and even repetition, a finding consistent with the notion that task characteristics influence likelihood of phonological activation and naming success, but contrary to the notion that there exist separate task-specific output systems. We conclude that Newton exhibits a unique pattern of deficits, which have theoretical relevance for the debate on the relationship between phonology and orthography, the role of automatic speech and the relationship between naming, reading and repetition.