Motivated semantic control: Exploring the effects of extrinsic reward and self-reference on semantic retrieval in semantic aphasia

Abstract

Recent insights show that increased motivation can benefit executive control, but this effect has not been explored in relation to semantic cognition. Patients with deficits of controlled semantic retrieval in the context of semantic aphasia (SA) after stroke may benefit from this approach since 'semantic control' is considered an executive process. Deficits in this domain are partially distinct from the domain-general deficits of cognitive control. We assessed the effect of both extrinsic and intrinsic motivation in healthy controls and SA patients. Experiment 1 manipulated extrinsic reward using high or low levels of points for correct responses during a semantic association task. Experiment 2 manipulated the intrinsic value of items using self-reference, allocating pictures of items to the participant ('self') or researcher ('other') in a shopping game before participants retrieved their semantic associations. These experiments revealed that patients, but not controls, showed better performance when given an extrinsic reward, consistent with the view that increased external motivation may help ameliorate patients' semantic control deficits. However, while self-reference was associated with better episodic memory, there was no effect on semantic retrieval. We conclude that semantic control deficits can be reduced when extrinsic rewards are anticipated; this enhanced motivational state is expected to support proactive control, for example, through the maintenance of task representations. It may be possible to harness this modulatory impact of reward to combat the control demands of semantic tasks in SA patients.

Keywords: Aphasia; Motivation; Reward; Self-reference; Semantic; Stroke.

Figure 1

Patient lesion analyses, including (a) a lesion overlap map for ten SA patients in the current study, created using manual segmentation in MRICron. This map shows lesion overlap in six or more patients, with the color of the lesioned area corresponding to the number of affected cases (bottom left). We assessed the extent of overlap between patient lesions and term‐based meta‐analytic maps from Neurosynth for the terms (b) ‘semantic’ (1031 studies), (c) ‘demands’ (596 studies), and (d) ‘reward’ (922 studies). Neurosynth maps are colored according to impact by lesions across the sample, with brighter areas reflecting those more often implicated in lesions. Each map was formatted in MRICron. We present (e) the mean percentage of each map lesioned across patients, with standard error of the mean error bars.

Figure 2

Experiment 1 procedure. (1) Each block was preceded by a high reward or low reward graphic. (2) Participants made thematic associations, either with strong or weak associations. Participants were provided with feedback as to whether their response was (3) correct or (4) incorrect. (5) Following each block, participants completed ratings of enjoyment, confidence, and focus.

Figure 3

Experiment 1 bar graphs for (a) mean proportion of correct response (dotted line reflects chance performance, 0.33) and (b) self‐report ratings across reward conditions, participant groups, and association strength, with standard error of the mean error bars.

Figure 4

Experiment 2 procedure. (1) One item from each pair of probe pictures was allocated to the participant and the other to the researcher. (2) Participants completed strong and weak associations for both the self‐ and other‐allocated items in each pair. (3) After each trial, participants gave a rating of response confidence. (4) Participants were tested on source memory for 30 pictures.

Figure 5

Experiment 2 bar graphs for (a) A’, a non‐parametric signal detection measure of recognition memory based on the proportion of correct hits and false‐positives, (b) mean proportion of correct responses in the semantic task (dotted line = chance), and (c) mean self‐report ratings of response confidence, with standard error of the mean error bars.