The dual origin of lexical perseverations in aphasia: Residual activation and incremental learning
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1
Johns Hopkins University, Department of Neurology, United States
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2
Johns Hopkins University, Department of Cognitive Science, United States
Lexical perseveration (LP), the inappropriate repetition of a previous response, is not uncommon in aphasia. Two underlying mechanisms have been proposed: the “residual activation account” (Cohen & Dehaene, 1998) posits that a response is repeated because it has residual activation, whereas the “learning account” (Oppenheim, Dell, & Schwartz, 2010) proposes that a response is repeated because the connections from the semantic features (e.g., pet) to the lexical item (e.g., “cat”) have been strengthened. Thus, when the same feature is activated by a different stimulus (e.g., “dog”), the earlier response may be repeated. Both accounts predict a decreasing likelihood of LP as the distance between the perseveration and its source increases, but only the learning account predicts that LP should be more sensitive to the number of intervening items (lag) than to time. Empirical data from the blocked cyclic naming task have confirmed this prediction (Hsiao, Schwartz, Schnur, & Dell, 2009). However, this task (a) involves many repetitions of the same items, and (b) groups items into semantically-related blocks, two characteristics which may encourage semantically-related perseverations. Using a very large set of picture naming trials with no items repeated within a session and at least 12 items between semantically-related pictures, we tested the predictions of these theories in seven individuals with aphasia: the residual activation account predicts perseveration of recent responses (highest probability at lag 2; Hsiao et al., 2009) regardless of their relationship to the current target, while the learning account predicts semantically-related perseverations even at long lags.
Participants were included if they had semantic-to-lexical mapping problems as evidenced by a predominance of lexical (as opposed to phonological) errors on the Philadelphia Naming Test (PNT, N = 175; Table 1). All participants completed an additional long picture naming task (N = 444 pictures on two occasions for a total of 888 trials) over 5–6 sessions. Chance was calculated once using a lag-2 window and once using a longer window encompassing all trials before the LP. Table 1 shows perseveration rates and lags over all trials (total N = 1063). Two findings were noteworthy:
1. Two distinct types of LPs were identified (Figure 1a): unrelated LPs with short lags (Mdn = 6) consistent with residual activation, and semantically-related LPs with long lags (Mdn = 36) consistent with learning.
2. The proportion of the LP types identified in (b) was predicted by the overall severity of the participant’s deficit, as shown by strong Spearman correlations between PNT error rates and both the ratio of semantically-related to unrelated LPs (r = -.929, p = .007; Figure 1b) and the ratio of short- to long-lag LPs (r = .929, p = .007; Figure 1c).
The results suggest two origins for LPs in aphasia: one due to residual activation of recent responses, and one due to incremental changes to semantic-to-lexical connections. As the weights of these connections get weaker, the proportion of LPs attributable to residual activation of recent responses increases.
Acknowledgements
This work was supported in part by the Therapeutic Cognitive Neuroscience Fund.
References
Cohen, L., & Dehaene, S. (1998). Competition between past and present. Assessment and interpretation of verbal perseverations. Brain, 121(9), 1641–1659. https://doi.org/10.1093/brain/121.9.1641
Hsiao, E. Y., Schwartz, M. F., Schnur, T. T., & Dell, G. S. (2009). Temporal characteristics of semantic perseverations induced by blocked-cyclic picture naming. Brain and Language, 108(3), 133–144. https://doi.org/10.1016/j.bandl.2008.11.003
Oppenheim, G. M., Dell, G. S., & Schwartz, M. F. (2010). The dark side of incremental learning: A model of cumulative semantic interference during lexical access in speech production. Cognition, 114(2), 227–252. https://doi.org/10.1016/j.cognition.2009.09.007
Keywords:
Aphasia,
perseveration,
Incremental Learning,
picture naming,
Language production
Conference:
Academy of Aphasia 56th Annual Meeting, Montreal, Canada, 21 Oct - 23 Oct, 2018.
Presentation Type:
oral presentation
Topic:
not eligible for a student prize
Citation:
Hepner
CR and
Nozari
N
(2019). The dual origin of lexical perseverations in aphasia: Residual activation and incremental learning.
Conference Abstract:
Academy of Aphasia 56th Annual Meeting.
doi: 10.3389/conf.fnhum.2018.228.00010
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Received:
16 Apr 2018;
Published Online:
22 Jan 2019.
*
Correspondence:
Mr. Christopher R Hepner, Johns Hopkins University, Department of Neurology, Baltimore, United States, chris@crhepner.com