Background: Bistable images (or ambiguous images) have the chance to be interpreted in two different ways. Owing to its physical features, this type of images offers two independentvisual perceptswhich are associated with top-down and bottom-up modulating perceiving processes. It has been also stated that tones of voice can operate as semantic modulators in such a way that the voice itself can exert a top-down influence on the way an observer perceives a bistable visual stimulus, regardless of the understanding of the speech (words meaning) that operates as a modulating factor. Objective: The study that is outlined here aimed at establishing the modulating effect of tones of voice on the interpretation of a bistable image. The speech understanding variable was taken into consideration as a covariate. Method:45 participants viewed twice the image My girlfriend or my mother-in-law whilst listening separately to a voice of a young woman and a voice of an old woman. The first time each participant observed the image on a screen of a fixed eye-tracker device of 60 Hz. (for 20 seconds). They listened to the audio of an old woman speaking while viewing the bistable image. The second time, the image was the same, but the auditory stimulus was a young woman speaking. The auditory monologues of both the old woman and the young woman were taken from French videos. These audios were randomly presented exchanging their order so as to have a counterbalance which could control the presentation order variable. This study was an experimental-intrasubject one. Results: There were significant differences between the duration of the congruent visual understandings and the duration of the incongruous visual interpretations. The results show a statistically significant difference in favor of the modulated perception, that is, that a differential result was found in favor of the image relating to the semantically-congruent percept(congruent with the audio)in relation to the semantically-incongruous image. In addition, the understanding of the modulating voices (meanings of words) did not imply an effect on the visual interpretations that were congruent with the auditory modulator. Conclusions: Auditory stimulation can provide congruent semantic contexts with every possible interpretation of a bistable image. The use of voice tones as semantic modulators may have the possibility of exerting an effect on the decoding of bistable images, regardless of the understanding of the content of the pronounced words.
