Measuring Pupillometry during the Comprehension of Conventional Metaphors

Abstract

Conventional metaphors (e.g., "a sweet compliment") are very common in everyday speech. Previous neural and physiological studies suggest that metaphorical stimuli are more emotionally engaging than matched literal stimuli (e.g., "a kind compliment") but additional research is needed to compare metaphorical with concrete stimuli (e.g., "a sweet candy"). A pupillometry study was conducted in order to compare two hypotheses: an increase in engagement may be due to (1) the figurative use of a word or phrase (metaphoricity), or (2) the availability of a concrete image (imageability). To test these hypotheses, 60 sentence triples were created, each consisting of a Metaphorical sentence (e.g., "The actor gave his co-star a sweet compliment"), a Literal sentence (e.g., "The actor gave his co-star a kind compliment"), and a Concrete sentence (e.g., "The actor gave his co-star a sweet candy"). Sentences were normed on Amazon Mechanical Turk for gradient judgments of metaphoricity, imageability, and seven other features. 66 participants listened to one sentence from each triple while their pupil sizes were recorded. Pupil dilation was used as a measure of emotional and cognitive engagement and pupillary synchrony was used as a measure of emotional salience. Verbatim memory was also measured to determine if greater engagement for Metaphorical sentences would correspond to greater verbatim memory. Metaphorical sentences elicited greater pupil dilation starting at the metaphorical key phrase until the end of the sentence but did not elicit greater pupillary synchrony or verbatim memory. Overall, the pupil dilation results support the metaphoricity hypothesis: metaphorical sentences are more engaging due to their figurative use of words and phrases.