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Authors
Nora Koster; Uwe Mattler; Thorsten Albrecht

Visual experience forms a multidimensional pattern that is not reducible to a single measure: Evidence from metacontrast masking

publication date
March 2020
Category
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Abstract/Introduction

A metacontrast masking paradigm was employed to provide evidence for the richness and diversity of our visual experience. Square- and diamond-shaped targets were followed by square- and diamond-shaped masks at varying stimulus onset asynchronies (SOAs), resulting in shape-congruent and shape-incongruent trials. In Experiment 1, participants reported in each trial how they perceived target and mask. After extended training, seven different aspects of the target could be distinguished as specific percepts in this metacontrast masking paradigm. These percepts encompass aspects including the temporal distance between both stimuli, the perceived contrast of the target, and motion percepts resulting from the interplay between the target and mask. Participants spontaneously reported each of these percepts, and the frequency of reports varied systematically with SOA and the congruency between target and mask. In Experiment 2, we trained a new group of participants to distinguish each of these target percepts. Again, the frequency of reports of the specific percepts varied with SOA and congruency, just as in Experiment 1. In a last session, we measured objective discrimination performance yielding the typical individually different masking functions across SOAs. An examination of the relation between the frequencies of reports of subjective percepts and objective discrimination performance revealed multiple dissociations between these measures. Results suggest a multidimensional pattern of subjective experiences under metacontrast, which is reflected in dissociated subjective and objective measures of visual awareness. As a consequence, awareness cannot be assessed exhaustively by a single measure, thus challenging the use of simple one-dimensional subjective or objective measures in visual masking.


Conclusion/Results

We developed a new approach to examine the phenomenological experience of simple visual stimuli that takes into account requirements of naturalized phenomenology to overcome the limitations of previous phenomenological approaches. We applied this approach to investigate the richness of phenomenological experience in a metacontrast masking paradigm with simple stimuli. First, we collected spontaneous reports of percepts of naïve observers who were only trained to focus on the target stimulus in the metacontrast sequence. The frequency of reports of individual percepts was systematically modulated by the experimental variables SOA and congruency. Second, we had naïve raters classify the individual descriptions of the percepts into seven percept categories that we found in a scattered literature on metacontrast. Third, we trained a new sample of participants to report the appearance of each of the seven percepts and observed how the frequency of reports of each percept varied with SOA and congruency. The correspondence between the characteristics of the spontaneous and the instructed reports indicates that we are reliably measuring specific stable entities and thus validates our approach, although these entities are subjective experiences that vary considerably among participants. The comparison of the characteristics of the percepts with the characteristics of similar reports in the literature revealed that our approach produces meaningful results. Findings provide evidence for the view that phenomenal consciousness forms a multidimensional pattern that is not reducible to a single measure. This multidimensionality has far-reaching implications: First, any measure of consciousness that claims to be exhaustive has to capture a multivariate pattern of visual experiences, which cannot be done by single one-dimensional subjective or objective scales. Second, any approach to demonstrate a dissociation between indirect and direct effects of masked primes has to consider carefully, which dimension of the multivariate pattern is the most relevant. Third, multidimensionality provides new boundary conditions for theory building. A comprehensive model of masking must allow for multiple visual experiences and must be able to explain different masking time courses for multiple stimulus dimensions.


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