An implicit representation of stimulus ambiguity in pupil size

Area of Science:

• Auditory perception
• Cognitive neuroscience
• Psychophysics

Background:

• Perceptual systems navigate ambiguous sensory input to guide behavior.
• While observers often recognize perceptual uncertainty, they can also fail to do so consciously.

Purpose of the Study:

• To investigate if physiological measures, specifically pupil dilation, reflect stimulus ambiguity even without conscious awareness.
• To explore the relationship between behavioral uncertainty and pupil responses using an auditory ambiguous stimulus.

Main Methods:

• Utilized the tritone paradox, an auditory stimulus known to induce ambiguous pitch perception.
• Conducted two experiments measuring behavioral responses and pupil dilation.
• Quantified stimulus ambiguity using the entropy of behavioral responses.

Main Results:

• Behavioral responses indicated listeners could not explicitly access the stimulus ambiguity.
• Pupil dilation was significantly larger for more ambiguous stimulus presentations.
• Stimulus ambiguity, indexed by response entropy, predicted pupil size independently of confidence judgments.

Conclusions:

• Physiological measures like pupil dilation can implicitly track stimulus ambiguity.
• The brain represents stimulus ambiguity even when individuals lack explicit awareness.
• Pupil dilation serves as a physiological correlate of implicit perceptual uncertainty.