Linguistic and nonlinguistic processing speed across age-matched normal healthy controls and individuals with left-hemisphere damage, with and without aphasia

ABSTRACT

Background

Slowed language production and comprehension in people with aphasia (PWA) is frequently cited as a characteristic of the disorder, even after full recovery. However, results supporting the existence of slowness are inconsistent and the mechanisms are unclear. Previous research has failed to determine the neurocognitive locus of the slowing and whether it is due to left hemisphere damage, general aging, or language-specific mechanisms. The goals of this study are: (1) to explore whether reduced processing speed is present and specific to the presence of aphasia or due to left-hemisphere damage more generally and (2) whether it is specific to the linguistic domain of cognition.

Results

The results of the mixed effects model revealed significant main effects for groups and domains, and no significant interactions among groups or between domains. The two brain-damaged groups exhibited significantly longer processing times across tasks compared to the NHC group. The processing speed of the PWA group was significantly longer than that of the LHD group across simple perceptual and more cognitively complex tasks. Groups were not significantly different on three nonlinguistic sensory-motor tasks.

Conclusions

Left-hemisphere damage-related slowing, as well as aphasia-additive slowing, was demonstrated as evidenced by significant differences between the two brain-damaged groups and between these two groups and the NHC group. Therefore, the observed slowing in the PWA group appears to be due to both brain-damage-related and aphasia-additive slowing. Domain-specificity was not observed as evidenced by significant slowing on both linguistic and nonlinguistic tasks in both brain-damaged groups compared to the performance of the NHCs.

KEYWORDS:

• Processing speed
• left-hemisphere damage with and without aphasia
• aphasia additive slowing
• brain damage related slowing

Acknowledgments

This research was carried out with the support of Dr. Sheila Pratt and Dr. Connie Tompkins for the space for the partial data collection. The authors are grateful to audiences at the 2017 ASHA Conference and the 2018 Clinical Aphasiology Conference for helpful discussion, and to Dr. James Becker for helpful comments as a dissertation committee member. The authors are particularly grateful to all the participants who generously gave of their time and mental effort.

Disclosure statement

No potential conflict of interest was reported by the authors.

Disclaimer

The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs or the United States government.

Supplementary material

Supplemental data for this article can be accessed here.

Notes

1. Response time can be defined as the total time to respond to a stimulus, while reaction time can be defined as the interval from the presentation of the stimuli to the beginning of the response. Response time therefore subsumes reaction time, because it is composed of reaction time and movement time. However, the two terms have often been used interchangeably.

2. The impact of a limited time mechanism can be measured in dual-task conditions, wherein overlapping or competing information processing between early and later operations engenders slowed processing (c.f., Hula & McNeil, 2008)

3. The nonlinguistic and linguistic simple reaction time tasks were presented with the instruction to respond “as quickly as possible”. This procedure is susceptible to motivational factors, and could be affected by other factors such as age, gender, education, and ethnicity (Miller et al., 1993). Therefore, the instruction for all simple reaction tasks was provided consistently and uniformly to make the response equally susceptible to those potential factors.