Stimulus categorization by brain-damaged patients

Patients with localized insult to the right hemisphere, or to either the anterior or the posterior portion of the left hemisphere, as well as neurologically intact controls, evaluated stimuli on a seven-point rating scale for their degree of category membership. The stimuli were taken from one of two continua, one composed of fruit and vegetable items, and the other of items differing in hue and shape. Different subsets of stimuli provided different contexts for the judgments of category membership. The two left-hemisphere groups showed anomalies in categorizing the fruit and vegetable items but not the perceptual items, while the reverse was true for the right-hemisphere patients. Moreover, both left-hemisphere groups demonstrated context effects in their judgments of the representativeness of the fruit and vegetable items, but differed in the way in which they responded to changing contexts. Left posterior patients demonstrated weak category boundaries and even reclassified items. In contrast, patients with left anterior damage showed highly categorical responses and less differentiation of items within a category. All groups showed striking context effects in judgments of perceptual items in terms of changes in representativeness ratings and the location of a category boundary. Alternative interpretations of the results are offered.     

Dissociation between the mental rotation of visual images and motor images in unilateral brain-damaged patients

Deficits in the mental rotation of body parts and of external objects can be doubly dissociated (Rumiati, Tomasino, Vorano, Umiltà, & De Luce, 2001; Sirigu & Duhamel, 2001; Tomasino, Rumiati, & Umità, in press). The aim of this study was to replicate this finding and to then investigate the relevance of the specific hemispheres in these deficits. Nine patients with unilateral lesions (five in the Left Hemisphere and four in the Right) and 20 control subjects, performed a single task requiring mental rotation of hands, and two tasks requiring mental rotation of external objects. RH patients were impaired in the rotation of external objects, but showed intact performance on the rotation of hands; the opposite pattern was found for LH patients. These results support the view that the LH contributes to the mental rotation of hands, recruiting processes specific to motor preparation, while the RH is specialized for mental rotation of external objects.     

The analysis of drawing from memory performance in brain-damaged patients

The drawing from memory task is frequently used in cognitive neuropsychology to investigate visual processing impairments. However, in surprising contrast to most other neuropsychological tests, the analyses of results on this task are most often based solely on qualitative judgements about the normality of a patient's performance. In most case reports, these judgements are not made with reference to normative data and are not made by individuals who are impartial with respect to the study (that is, using a blind rating procedure). There are several grounds for arguing that such analyses are inadequate. First, seemingly abnormal drawings made by a patient may well be within the range of performance shown by control subjects. Second, judgments that are not based on a blind rating procedure are likely to be influenced by knowledge about the patient's performance on other tasks. We describe an alternative assessment procedure that addresses both of these concerns.     

Inference deficits in right brain-damaged patients

The inferential reasoning ability of right hemisphere-damaged (RHD) patients was tested by presenting pairs of sentences which were to be treated as single, integrated units. The two sentences treated together made one interpretation likely (a correct inference); one of the sentences in isolation encouraged a different interpretation (an incorrect inference). The position of the misleading sentence was systematically varied. Results showed that, in contrast to normal controls, RHD patients have more trouble answering inference questions, especially those concerning incorrect inferences, than answering questions about the factual content of the passages. Also, RHD patients made significantly more errors when the misleading information was contained in the first rather than in the second sentence; this finding indicates that these patients have difficulty revising previously acquired knowledge in light of new information. These results suggest the impairment of several components of normal discourse processing subsequent to right hemisphere brain damage.     

Comprehension of humorous and nonhumorous materials by left and right brain-damaged patients

Right hemisphere-damaged (RHD) and left hemisphere-damaged (LHD) aphasic patients were tested on a nonverbal cartoon completion task that included a humorous (Joke) and a nonhumorous (Story) condition. In both conditions, RHD patients performed worse than LHD patients. More importantly, the qualitative difference between the errors produced by the two groups suggests that right and left hemisphere brain damage impairs different components of narrative ability. RHD patients showed a preserved sensitivity to the surprise element of humor, and a diminished ability to establish coherence. Conversely, LHD patients, when they erred, showed an impaired sensitivity to the surprise element of humor, and a preserved ability to establish coherence by integrating content across parts of a narrative. These results suggest that the observed humor comprehension deficits of RHD patients result specifically from right hemisphere disease and not from brain damage irrespective of locus. The performances of the RHD and LHD patients groups together support a separation of narrative ability from the traditional aspects of language ability typically disrupted in aphasia.     

Story processing in right-hemisphere brain-damaged patients.

The understanding of stories requires sensitivity to structural aspects of narrative, the emotional content conveyed by the narrative, and the interaction between structural and emotional facets of the story. Right-hemisphere-damaged (RHD) and normal control subjects performed a number of different analytic tasks which probed their competence at story comprehension. Results revealed that RHD subjects perform at a level comparable to that of normal controls with stories that follow a canonical form and that they show few difficulties with structural aspects of narrative. Contrary to expectation, they are strongly influenced by the "interest" level of a story and by other factors that tap emotional sensitivity. Findings are discussed in terms of the processing and arousal mechanisms which may give rise to the observed pattern of difficulties in RHD patients.     

Story arrangement ability in right brain-damaged patients.

The purpose of the present study is to explore the role of an explicit expression of macrostructure in facilitating performance on a Story Arrangement Task. Subjects were presented with a series of sentences which they were required to arrange into a coherent paragraph. Half of the items were preceded by a theme sentence containing the framework or macrostructure of the paragraph, while the items without theme sentences required subjects to formulate their own macrostructure in a bottom-up fashion. Results of the study support the hypothesis that the presence of a theme sentence facilitates performance on the Story Arrangement Task for non-brain-damaged individuals (NBDs) and left brain-damaged patients (LBDs), but not for right brain-damaged patients (RBDs). This suggests that RBDs are impaired in their ability to recognize and benefit from explicit thematic statements in narratives. Other discourse-level deficits in RBDs are discussed in the light of these findings. The performance of LBDs on such tasks is also discussed.     

Semantic disorders of auditory language comprehension in right brain-damaged patients

A test of auditory language comprehension was given to 110 right brain-damaged patients and to 94 normal controls in order to check if patients with lesions of the right (nondominant) hemisphere make a significantly higher number of semantic errors than normals. Confirmation of the hypothesis was obtained, but the relationship between semantic errors and lesion of the right hemisphere did not seem a simple and direct one. In fact, most of the lexical-semantic errors were due to associated variables (such as unilateral spatial agnosia and general mental deterioration) and not to the lesion of the right hemisphere per se. These data do not suggest a specific semantic capacity of the nondominant hemisphere but rather stress the fragility of the lexical-semantic organization at the cortical level.This work was assisted by a grant from C.N.R. (Consiglio Nazionale delle Ricerche).     

The use of pronoun anaphora and speaker mood in the interpretation of conversational utterances by right hemisphere brain-damaged patients.

Understanding utterances in conversations requires a listener to weigh the disparate pieces of information present in a discourse. In this study, we examined how right hemisphere brain-damaged (RHD) patients and non-brain-damaged control subjects interpreted responses to questions concerning the location of a person (e.g., "Where's Dad?"). Stimulus vignettes included variation on three factors relevant to discourse comprehension: the mood of a speaker, the plausibility of the answer to a question, and whether the answer contained an anaphoric pronoun linking the response to the preceding question. Relative to the control subjects, the RHD patients made greater than normal use of the presence/absence of an anaphoric pronoun in their utterance interpretations, less than normal use of the speaker's mood, and marginally less than normal use of a response's plausibility. These data show how RHD patients rely on their largely intact linguistic abilities when understanding discourse and how their comprehension goes awry due to their reduced appreciation of other essential aspects of natural communication. The discussion focuses on the variable roles of speaker mood, plausibility, and pronoun anaphora in supporting inferences about a speaker's intended meaning and on the selective nature of RHD patients' impairment in this domain.     

Characteristics of recovery of drawing ability in left and right brain-damaged patients

Drawings of a "person" were obtained from 21 patients with left brain damage (LBD) and 13 patients with right brain damage (RBD) at hospital discharge and 1 month postdischarge, corresponding to 2-4 and 6-8 weeks postonset, respectively. Early LBD drawings were simplistic and often incoherent. Most were placed in the upper left quadrant of the page. RBD drawings were scattered, fragmented, and elaborately detailed. Many showed evidence of left-sided neglect. The resolution of drawing disability also differed between the two groups: LBD subjects recovered drawing abilities more rapidly and more completely than RBD subjects. These differences in drawing characteristics and in the resolution of drawing disability were discernable for experienced neuropsychologists.