P300 Modulation by Task Difficulty in Probabilistic Reward Learning

Mathiske, Carlotta Mae (2025) P300 Modulation by Task Difficulty in Probabilistic Reward Learning. Master thesis, Psychology.

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Abstract

The P300 event-related potential (ERP) is a neural marker often linked to cognitive effort, typically showing reduced amplitude and increased latency with rising task difficulty. While these effects are well-established in structured cognitive tasks, less is known about how P300 responds during probabilistic reward learning, where difficulty arises naturally from uncertain outcomes. This study tested whether task difficulty modulates P300 during a probabilistic reward learning task and compared learning in gain- vs. loss-focused contexts. Twenty-three participants learned reward probabilities (0.7, 0.5, or 0.3) of three stimuli through feedbackbased trial and error, followed by a testing phase requiring that they select one of two stimuli without feedback. Task difficulty was manipulated by varying reward probability differences and the availability of the highest-reward option. Results showed that participants learned to choose higher-reward options over time but struggled to distinguish between options with similar reward probabilities. Accuracy declined and reaction times increased with difficulty. Yet, reaction times did not systematically decrease over time, suggesting sustained deliberation. Moreover, contrary to expectations, participants responded fastest to the most rewarding stimulus but were slowest to avoid the least rewarding one, suggesting that hesitation and uncertainty, not learning strength, drove slower decisions. Loss-focused learning improved accuracy, particularly in difficult trials. Despite behavioral effects, P300 amplitude and latency remained unchanged, suggesting that difficulty-related effects in this task were either driven by response conflict rather than cognitive resource depletion or that the overall task difficulty was too high to elicit measurable differences in neural processing.

Item Type:	Thesis (Master)
Supervisor name:	Lorist, M.M. and Span, M.M.
Degree programme:	Psychology
Differentiation route:	Cognitive Psychology and Psychophysiology (CPP) [Master Psychology]
Date Deposited:	02 Sep 2025 07:02
Last Modified:	02 Sep 2025 07:02
URI:	http://gmwpublic.studenttheses.ub.rug.nl/id/eprint/5914

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