Abstract
Previous research revealed stable individual gaze biases along several semantic dimensions when viewing complex scenes. For instance, some observers have a stronger tendency to fixate faces while others fixate text more often. However, it is unclear what proportion of individual gaze differences towards objects in complex scenes is explained by these known dimensions. Here, we used a novel approach to analyse individual differences in gaze behaviour by computing ‘dimension-agnostic’ (dis-)similarities between observers. We analysed an eyetracking data set of N = 103 subjects, who freely viewed 700 complex scenes, depicting > 5000 objects. To estimate the noise ceiling of stable individual differences independently of a priori dimensions, we computed the similarity (Euclidean distance) of dwell times across all objects for each pair of observers. These pairwise similarities were highly consistent across independent subsets of images (R2 = .81). To explore how much of these stable differences can be explained by known individual gaze tendencies towards semantic dimensions, we determined individual fixation tendencies towards objects of 5 semantic dimensions and computed the similarity between each pair of observers for each dimension. We then fitted a cross-validated ridge regression model, predicting overall observer similarity from similarity matrices for each dimension. Results indicated that known dimensions captured 27% of the explainable variance in object fixations. Individual tendencies to fixate Faces (β = .22) and Text (β= .17) carried the highest weights, followed by fixation biases for Taste (β= .11), Motion (β= .10) and Touched (β= .07). Together, our findings suggest that individual tendencies along known semantic dimensions account for a substantial part of individual differences in object fixations. At the same time, most of the explainable variance in object fixations is not captured by these dimensions. We currently explore further dimensions, including individual biases for lower level image features and saccadic behaviour.