Non-verbal semantic impairment in semantic dementia

Abstract

The clinical presentation of patients with semantic dementia is dominated by anomia and poor verbal comprehension. Although a number of researchers have argued that these patients have impaired comprehension of non-verbal as well as verbal stimuli, the evidence for semantic deterioration is mainly derived from tasks that include some form of verbal input or output. Few studies have investigated semantic impairment using entirely non-verbal assessments and the few exceptions have been based on results from single cases ([3]: Breedin SD, Saffran EM, Coslett HB. Reversal of the concreteness effect in a patient with semantic dementia. Cognitive Neuropsychology 1994;11:617-660, [12]: Graham KS, Becker JT, Patterson K, Hodges JR. Lost for words: a case of primary progressive aphasia? In: Parkin A, editor. Case studies in the neuropsychology of memory, East Sussex: Lawrence Erlbaum, 1997. pp. 83-110, [21]: Lambon Ralph MA, Howard D. Gogi aphasia or semantic dementia? Simulating and assessing poor verbal comprehension in a case of progressive fluent aphasia. Cognitive Neuropsychology, (in-press). This study employed sound recognition and semantic association tasks to investigate the nature of the verbal and non-verbal comprehension deficit in 10 patients with semantic dementia. The patients were impaired on both verbal and non-verbal conditions of the assessments, and their accuracy on these tasks was directly related to their scores on a range of other tests requiring access to semantic memory. Further analyses revealed that performance was graded by concept and sound familiarity and, in addition, identified significant item consistency across the different conditions of the tasks. These results support the notion that the patients' deficits across all modalities were due to degradation within a single, central network of conceptual knowledge. There were also reliable differences between conditions. The sound-picture matching task proved to be more sensitive to semantic impairment than the word-picture matching equivalent, and the patients performed significantly better on the picture than word version of a semantic association test. We propose that these differences arise directly from the nature of the mapping between input modality and semantic memory. Words and sounds have an arbitrary relationship with meaning while pictures benefit from a degree of systematicity with conceptual knowledge about the object.

The perirhinal cortex modulates V2 activity in response to the agreement between part familiarity and configuration familiarity

“…Other evidence indicates a role for the temporal pole in accessing semantic information across a wide range of stimulus types (Bright et al, 2005;Lambon Ralph et al, 2008). Consistent with this, semantic dementia, a neurodegenerative condition characterized by progressive deterioration of semantic knowledge is associated with atrophy to the temporal poles (Bozeat et al, 2000;Rogers et al, 2004). We note that patients with semantic dementia are typically impaired at object decision (e.g., judging whether drawings represented real or nonsense objects; Patterson et al, 2006), as well as perceptual discrimination of complex objects (Barense et al, 2010b).…”

A role for left temporal pole in the retrieval of words for unique entities

“…Lesions that lead to impaired retrieval of the names of persons affect primarily the left temporal cortex and its subcortical connections, while lesions that impair the recognition of those unique persons affect primarily the right anterior temporal and occipito-temporal cortices, as demonstrated by lesion studies [Damasio et al, 1990a[Damasio et al, , 1990bEllis et al, 1989; and by reports of "progressive prosopagnosia" associated with progressive atrophy of the right anterior temporal lobe [Tyrrell et al, 1990;Evans et al, 1995;Snowden, 1999]. Some authors [e.g., Bozeat et al, 2000;Mummery et al, 2000] have noted that "semantic dementia," manifested by anomia and semantic memory loss, is associated with progressive atrophy of the left temporal lobe, which is usually conspicuous in the pole at the time of diagnosis. In addition, some stable, acquired lesions involving this area, usually a result of herpes simplex encephalitis, are also associated with semantic memory loss.…”

Object categorization: Reversals and explanations of the basic-level advantage.

“…In drawing tasks, patients frequently omit properties specific to a particular concept (e.g., the udder of a cow, the hump on a camel), but rarely do they omit properties common to the category superordinate (e.g., the eyes of the camel, the mouth of the cow; Bozeat et al, 2003). These and a host of other similar phenomena documented in SD (Adlam, Patterson, Rogers, Salmond, & Hodges, 2006;Bozeat, Lambon Ralph, Patterson, Garrard, & Hodges, 2000;Hodges, Spatt, & Patterson, 1999;Rogers, Lambon Ralph, Hodges, & Patterson, 2003, 2004 suggest that, as the conceptual knowledge system deteriorates, what is retained is increasingly restricted to the general and typical.…”