Noun-verb dissociation in aphasia: the role of imageability and functional locus of the lesion.

Aphasic patients occasionally manifest a dissociated naming ability between objects and actions: this phenomenon has been interpreted as evidence of a separate organization for nouns and verbs in the mental lexicon. Nevertheless Bird et al. [Bird, H., Howard, D., Franklin, S. (2000). Why is a verb like an inanimate object? Grammatical category and semantic category deficits. BrainandLanguage, 72, 246-309], suggested that the damage underlying noun-verb dissociation affects the corresponding semantic concepts and not the lexical representation of words; moreover, they claimed that many dissociations reported in literature are caused merely by a strong imageability effect. In fact, most authors used a picture-naming task to assess patients' naming ability, and due to the fact that this test involves the use of pictures to represent actions and objects, nouns were frequently more imageable than verbs [Luzzatti, C., & Chierchia, G. (2002). On the nature of selective deficit involving nouns and verbs. RivistadiLinguistica, 14, 43-71]. In order to overcome this drawback, we devised a new task - nouns and verbs retrieval in a sentence context (NVR-SC) - in which nouns and verbs have the same imageability rate. Patients' performance on this task is compared with that obtained by the same patients on a standard picture-naming task. Of the 16 aphasic patients with a selective verb deficit, as revealed by the picture-naming task, two continued to show dissociation in the NVR-SC task, while 14 did not. The data indicate that at least some patients have an imageability-independent lexical deficit for verbs. The functional locus/i of the damage is also considered, with particular reference to the lemma/lexeme dichotomy suggested by Levelt et al. [Levelt, W. J. M., Roelofs, A., & Meyer, A. S. (1999). A theory of lexical access in speech production. BehavioralandBrainSciences, 22, 1-75].

Visual and tactile length matching in spatial neglect.

Previous studies have shown that many patients with spatial neglect underestimate the horizontal extent of leftwardly located shapes (presented on screen or on paper) relative to rightwardly located shapes. This has been used to help explain their leftward biases in line bisection. In the present study we have tested patients with right hemisphere damage, either with or without neglect, on a comparable length matching task, but using 3-dimensional objects. The task was executed first visually without tactile contact, and second through touch without vision. In both sense modalities, we found that patients with neglect, but not those without, tended to underestimate leftward located objects relative to rightward located objects, differing significantly in this regard from healthy subjects. However these lateral biases were not as frequent or as pronounced as in previous studies using 2-D visual shapes. Despite the similar asymmetries in the two sense modalities, we found only a small correlation between them, and clear double dissociations were observed among our patients. We conclude that leftward length underestimation cannot be attributed to any one single cause. First it cannot be entirely due to impairments in the visual pathways, such as hemianopia and/or processing biases, since the disorder is also seen in the tactile modality. At the same time, however, length underestimation phenomena cannot be fully explained as a disruption of a supramodal central size processor, since they can occur in either vision or touch alone. Our data would fit best with a multiple-factor model in which some patients show leftward length underestimation for modality-specific reasons, while others do so due to a more high-level disruption of size judgements.