The Treachery of Images: Objects, Pictures, Words and the Role of Affordances in Similarity Judgements

Categorization is a fundamental cognitive strategy employed to ease information processing and to aid memory formation. Past research on how humans categorize objects has used images of objects as experimental stimuli. Results suggest these stimuli are categorized based on abstract linguistic concepts. Concurrently, studies in the past 10 years have found differences in the processing of images as compared to real-world objects. One proposed explanation is that these results are due to differences in the affordances of images versus objects. Using a similarity judgement paradigm, we have explored the effect of affordances in a categorization task including words (object names), images, and objects. Consistent with previous research, we found significant differences in how participants made similarity judgements of images and objects. Moreover, we found that similarity judgments using object names were much more similar to the judgments of pictures than of objects. An exploratory cluster analysis opens the possibility of framing such differences as affordance driven. These results suggest a need for more ecologically valid categorization tasks, more conservative inferences when using images as stimuli in these tasks, and the need for further exploring the role of affordances in categorization.

Similarity is as Similarity Does? A Critical Inquiry into the Effect of Thematic Association on Similarity

Leading theories of psychological similarity are based on the degree of match in semantic content between compared cases (i.e., shared features, low dimensional distance, alignable relations). Broader forms of semantic relatedness such as the degree of association between cases (e.g., egg and spatula) are generally not considered to contribute to similarity judgments. However, empirical work has demonstrated a behavioral tendency to choose associated pairs over proximal pairs (i.e., high semantic content overlap) in similarity judgement tasks. As a result, dual-process models have been proposed that posit thematic integration in addition to content match as component processes of similarity. The present experiments investigate the thematic association effect in similarity in order to more clearly determine whether such a theoretical redirection is warranted. An alternative viewpoint is that confusion between similarity and association is the cause of the reported thematic bias. Experiment 1 introduces a modified similarity judgement task and addresses the impact of task instructions as a potential causal factor underlying the thematic association effect on similarity. Experiment 2 specifically compares the novel similarity task to a traditional two-alternative, forced choice triad task. Experiment 3 addresses the possibility of bias in the stimulus sets used in Experiments 1 and 2. Across the experiments we find association-based responding to be much less prevalent than in previous demonstrations: the traditional finding of a thematic preference only occurred when participants were specifically asked to select based on associativity (“goes with”). Modifications to conventional methodology that minimize biasing factors clearly attenuate the effect of association on similarity. We interpret these findings as evidence that that the thematic association effect derives from intrusions on psychological similarity, not from an additional component intrinsic to psychological similarity.