Imageability effects on sentence judgement by right‐brain‐damaged adults

Abstract

Background: For decades researchers assumed visual image generation was the province of the right hemisphere. The lack of corresponding evidence was only recently noted, yet conflicting results still leave open the possibility that the right hemisphere plays a role. This study assessed imagery generation in adult participants with and without right hemisphere damage (RHD). Imagery was operationalised as the activation of representations retrieved from long‐term memory similar to those that underlie sensory experience, in the absence of the usual sensory stimulation, and in the presence of communicative stimuli. Aims: The primary aim of the study was to explore the widely held belief that there is an association between the right hemisphere and imagery generation ability. We also investigated whether visual and visuo‐motor imagery generation abilities differ in adults with RHD. Methods & Procedures: Participants included 34 adults with unilateral RHD due to cerebrovascular accident and 38 adults who served as non‐brain‐damaged (NBD) controls. To assess the potential effects of RHD on the processing of language stimuli that differ in imageability, participants performed an auditory sentence verification task. Participants listened to high‐ and low‐imageability sentences from Eddy and Glass (1981) and indicated whether each sentence was true or false. The dependent measures for this task were performance accuracy and response times (RT). Outcomes & Results: In general, accuracy was higher, and response time lower, for low‐imagery than for high‐imagery items. Although NBD participants' RTs for low‐imagery items were significantly faster than those for high‐imagery items, this difference disappeared in the group with RHD. We confirmed that this result was not due to a speed–accuracy trade‐off or to syntactic differences between stimulus sets. A post hoc analysis also suggested that the group with RHD was selectively impaired in motor, rather than visual, imagery generation. Conclusions: The disproportionately high RT of participants with RHD in response to low‐imagery items suggests that these items had other properties that made their verification difficult for this population. The nature and extent of right hemisphere patients' deficits in processing different types of imagery should be considered. In addition, the capacity of adults with RHD to generate visual and motor imagery should be investigated separately in future studies.