Universität zu Köln

Memis, Elif ORCID: 0000-0003-2388-4171 (2026). Contextual Influences in Visual Perception: Behavioural and Neural Insights into Size Representations. PhD thesis, Universität zu Köln.

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Abstract

In order to interpret incoming sensory input effectively, the visual system integrates multiple sources of information from the surrounding environment. Although many perceptual processes are often assumed to operate automatically, accumulating evidence suggests that they rely on complex and dynamic mechanisms. Building on previous work employing behavioural measures, neuroimaging, and predictive coding frameworks, this thesis investigates how contextual influences modulate size representations, with a particular focus on ensemble summary statistics. Study I examined whether implicitly coded objects contribute to perceived average size by manipulating contextual size information using Ebbinghaus inducers. The results demonstrated that rescaled objects influenced ensemble representations regardless of whether they were explicitly or implicitly coded, suggesting that contextual size modulation occurs relatively early in the visual processing stream and remains available for subsequent statistical computations. Study II extended these findings by showing that when two sets of stimuli are presented simultaneously, their perceived average sizes mutually influence each other through contrast-like interactions. Behavioural and functional results indicated that ensemble representations are processed in parallel but remain susceptible to contextual modulation from neighbouring ensembles, even when they are task-irrelevant. Together, these findings challenge models assuming independent or pooled ensemble processing and instead support a framework in which ensemble summary statistics interact dynamically through contextual comparison mechanisms. Overall, this thesis demonstrates that ensemble representations are not mere summaries of stimulus features but actively serve as contextual cues in size perception, highlighting the importance of context in shaping perceptual representations.

Item Type:	Thesis (PhD thesis)
Translated abstract:	Abstract Language UNSPECIFIED English
Creators:	Creators Email ORCID ORCID Put Code Memis, Elif e.memis@fz-juelich.de https://orcid.org/0000-0003-2388-4171 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-798092
Date:	2026
Language:	English
Faculty:	Faculty of Human Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > Forschungszentrum Jülich
Subjects:	Psychology
Uncontrolled Keywords:	Keywords Language visual perception English contextual modulation English size perception English
Date of oral exam:	5 February 2026
Referee:	Name Academic Title Weidner, Ralph Privatdozent Dr. Vossel, Simone Jun.-Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79809