The importance of multiple assessments of object knowledge in semantic dementia: The case of the familiar objects task

Abstract

Semantic dementia (SD) is characterized by a dramatic loss of conceptual knowledge about the meaning of words and the identity of objects. Previous research has suggested that SD patients' knowledge is differentially influenced by the disease and may decline at different degrees depending on a patient's everyday familiarity with certain items. However, no study has examined (a) semantic knowledge deterioration and (b) the potential significance of autobiographical experience for the maintenance of object concepts in the same cohort of SD patients by using comprehensive assessments of different aspects of object knowledge across an experience-based, distributed semantic memory network. Here, we tested four SD patients and three Alzheimer's disease (AD) control patients using a range of tasks – including naming, gesture generation, and autobiographical knowledge – with personally familiar objects or perceptually similar or different object analogs. Our results showed dissociations between performance on naming relative to other assessments of object knowledge between SD and AD patients, though we did not observe a reliable familiar objects advantage. We discuss different factors that may account for these findings, as well as their implications for research on SD.

Keywords:

• Semantic dementia
• Familiar objects
• Semantic memory
• Episodic memory
• Object knowledge

ACKNOWLEDGEMENTS

This work was supported by grants AG17586, AG15116, and NS44266 from the National Institutes of Health to MG. The authors would like to thank Katy Cross, Shaleigh Kwok, and Shweta Antani for their assistance in the collection of the neuropsychological assessment of the patients diagnosed at the Hospital of the University of Pennsylvania and Jamie J. Reilly and Christopher H. Ramey for valuable comments on earlier versions of this manuscript.

Notes

¹We note that the MMSE performance at the time of diagnosis of patient JR was lower than that of the other three patients. Although we acknowledge this difference, in the absence of any other alternative neurological diagnosis for this patient, we note that the patient's performance in all other tasks of interest was comparable to the other patients, hence we chose to include his data in the analyses we report in the present paper. To examine whether the exclusion of this patient would influence our results, we performed all analyses with and without this participant. Given that we found no differences between these analyses, in addition to the overall limited number of SD patients discussed in the literature on semantic deficits, we decided to report our results with all four patients.

²Our rationale for selecting a specific order of presentation of the experimental tasks relative to a random order had to do with potential fatigue effects on participants' performance toward the end of the experimental session, which might have jeopardized the validity of our findings for all tasks, given the limited number of participants included in the study. That is, we aimed to ensure that there would not be one or more participants' data that would have to be entirely excluded from one of the five tasks due to fatigue effects, which might have been the case if random task presentation was followed and which would have significantly reduced the power to detect differences within each task. We note that, with only one exception, all patients were able to complete the experimental session without interruptions, thus we do not reckon that fatigue effects differentially influenced patients' performance in any of the tasks.

³Patients' content word generation for each object was given to a group of age-matched healthy control participants who verified the relevance of the generated words for the object in question. Given the length of the related analyses, those results will not be presented in detail here, as they go beyond the scope of the present paper.

⁴To explore performance across all tasks including the script generation task, we converted each participant's overall score for each task, separately for each object category, to a z score and repeated all analyses; however, due to the small number of patients for z score analyses, none of these differences reached statistical significance.