Visual Attention Dynamics Entrain to an Auditory Beat: The Palimpsest Paradigm

We investigated how rhythmic auditory cues influence visual perception of dynamically presented, partially masked words. Participants were presented with an ever-changing array of multiple overlapping, semi-transparent five-letter words, in a stimulus we dubbed a “palimpsest”. These letter arrays mostly consisted of nonsense strings, but every two seconds, two actual words briefly appeared consecutively (and typically subliminally), superimposed upon the nonsense letter array. Participants were asked to name all words that they recognized. One group of participants observed only visual stimuli, while a second group additionally received an acoustic stimulus: a drum beat that was timed to co-occur with some, but not all, of the words in the array. Participants provided with this additional synchronized auditory information were able to detect more words from the array, and the words that they recognized were typically those that coincided with the dominant acoustic beat. This shows that when visually presented words are difficult to detect, acoustic cues can improve word recognition by dynamically focusing participants’ attention upon specific moments in time. We also found that the auditory rhythm continued to affect visual perception after the sound fade fades away. A third group heard the drum beat only for the first four seconds, after which it faded away for the remaining 76 seconds of a trial. Like the continuous beat in condition two, the transient acoustic rhythm continued to influence participants’ perception of the written words, even after its cessation. These results are consistent with the hypothesis that dynamic, temporal aspects of visual perception can be strongly influenced by periodic auditory input, and that this results from the entrainment of an endogenous multi-modal attentive process. The implications for neural models of dynamic attention are discussed.