What we perceive at any given time is not only determined by the input reaching our sensory organs in the present, but also by what we perceived in the recent past, a few seconds ago. Past information (or “perceptual history”) plays a ubiquitous role in perception, systematically affecting how we perceive sensory stimuli in the present. For example, a vertical line could appear tilted if we saw a tilted line a few seconds before. Similarly, a sequence of events – like a flashing light – might appear as more or less numerous than it actually is, depending on the sequences that we saw before it. This phenomenon, also named “serial dependence,” effectively makes a present object to appear more similar to an object we saw before than it actually is. Recent research has found that perceptual history affects every domain of visual perception, starting from the most basic aspects of a scene, like orientation, colour, or shape, to more complex attributes like face identity or emotions. This suggests that this phenomenon reflects a fundamental brain processing mechanism supporting our perception. Many aspects of the functioning of this mechanism however remain unknown. One important question that remains unaswered is whether the influence of perceptual history purely reflects the information conveyed by past sensory stimuli, or whether it may work in a predictive fashion. That is, based on what the past information predicts, rather than past information per se. The brain indeed is not a passive receptor of information, but constantly predicts future inputs to speed up and optimise the processing of incoming information. Additionally, another interesting question is whether perceptual history effects work only within each sensory modality – that is, a past visual image affecting a present visual image, but not a sound – or whether this phenomenon may work across different modalities. Our perception is inherently multi-sensory, and indeed the brain possesses specific mechanisms to combine information from different sensory modalities. For example, we immediately know that an object fell to the floor based on the sound it makes, without the need to actually see the event to know what happened. In the PreVis project, we sought to address the predictive nature of perceptual history effects in the context on multi-sensory perception, and particularly in vision and audition. Considering the fundamental nature of the brain mechanisms involved with perceptual history, and the ubiquitous effect that they play in our perception, understanding them is something extremely important to understand how our brain generates perception. This phenomenon may have indeed important implications in several contexts that require accurate decisions, like a medical doctor classifying imaging results. We know that a past image can affect how we perceive an image in the present, but could a sound affect it as well? And why? Is it because the brain is trying to predict what comes next? Is the effect limited to information that is currently relevant for a task, or also irrelevant information from different senses could bias our judgments? With PreVis, we addressed these questions to gain new insights into how human perception works and the influences contributing to it. This is expected to have an important impact in the scientific sector, allowing us to refine our understanding of perception and devise new theories that can capture it more accurately.
