Comprehension of Reversible Constructions in Semantic Aphasia
Background: Impairments in spatial processing show themselves not only in gnosis and praxis, but also in the language domain. Luria (1947) considered this deficit a characteristic feature of so-called semantic aphasia and explained the impaired comprehension of semantically reversible constructions in those patients by a disorder of the common spatial neuropsychological factor grounded in the temporal-parietal-occipital regions of the brain.
Aims: The aim of the present study was to experimentally test the possibility that individuals with semantic aphasia experience specific difficulties in extracting spatial relations from a linguistic form and rely instead on basic sensorimotor stereotypes to interpret reversible linguistic constructions.
Method & Procedures: Six individuals with semantic aphasia, 12 people with motor aphasia, 12 people with sensory aphasia, and 12 non-brain-damaged individuals performed a sentence-picture matching task; all participants were native speakers of Russian. Two types of reversible sentences were tested, each representing a direct and an inverted word order: prepositional (The boy is putting the bag in the box vs. The boy is putting in the box the bag) and instrumental (The grandmother is covering the scarf with the hat vs. The grandmother is covering with the hat the scarf). Irreversible sentences (The boy is putting the apple in the bag) served as control stimuli.
Outcomes & Results: Each group of participants performed better on irreversible than on reversible sentences. Within reversible sentences, an interaction between word order and construction type was found in individuals with semantic aphasia only. They performed more accurately in prepositional constructions with direct word order and in instrumental constructions with inverted word order – both are related to sensorimotor stereotypes reflecting interaction with objects in the real world. Although no such clear dissociation was found in other aphasia types, correlation analysis revealed the same effect in some participants with motor and sensory aphasia.
Conclusions: The findings confirm the importance of situational context for linguistic processing. First, if knowledge of the real world supports the unique interpretation of grammatical markers, it enhances processing in all tested cohorts of participants. Second, people with semantic aphasia consistently use sensorimotor stereotypes to compensate for their linguistic deficits. Since this was also found in some participants with other aphasia types, such a sensorimotor strategy might depend not on the damage to temporal-parietal-occipital areas as such, but on the intactness and overuse of left premotor regions suggested to be critical for motor and symbolic sequential processing (Luria, 1947).