Abstract
The ability to integrate auditory and visual information is critical for effective perception and interaction with the environment, and is thought to be abnormal in some clinical populations. Several studies have investigated the time window over which audiovisual events are integrated, also called the temporal binding window, and revealed asymmetries depending on the order of audiovisual input (i.e. the leading sense). When judging audiovisual simultaneity, the binding window appears narrower and non‐malleable for auditory‐leading stimulus pairs and wider and trainable for visual‐leading pairs. Here we specifically examined the level of independence of binding mechanisms when auditory‐before‐visual vs. visual‐before‐auditory input is bound. Three groups of healthy participants practiced audiovisual simultaneity detection with feedback, selectively training on auditory‐leading stimulus pairs (group 1), visual‐leading stimulus pairs (group 2) or both (group 3). Subsequently, we tested for learning transfer (crossover) from trained stimulus pairs to non‐trained pairs with opposite audiovisual input. Our data confirmed the known asymmetry in size and trainability for auditory–visual vs. visual–auditory binding windows. More importantly, practicing one type of audiovisual integration (e.g. auditory–visual) did not affect the other type (e.g. visual–auditory), even if trainable by within‐condition practice. Together, these results provide crucial evidence that audiovisual temporal binding for auditory‐leading vs. visual‐leading stimulus pairs are independent, possibly tapping into different circuits for audiovisual integration due to engagement of different multisensory sampling mechanisms depending on leading sense. Our results have implications for informing the study of multisensory interactions in healthy participants and clinical populations with dysfunctional multisensory integration.
Highlights
Most events in the environment tap into different sensory systems at the same time
Previous research using a variety of tasks and stimuli to investigate temporal audiovisual integration has shown that humans display a certain degree of tolerance to audiovisual asynchrony and that such tolerance is typically greater for asynchronous stimulus pairs where visual stimulus leads (VA) compared to those where auditory stimulus leads (AV) (e.g., Conrey & Pisoni, 2006; van Eijk et al, 2008; Stevenson & Wallace, 2013). Notwithstanding these observations, auditory-before-visual and visual-before-auditory integration may be regarded as part of a continuum, implying that the AV and VA temporal binding window (TBW) are two sides of the same coin, with perception of audiovisual simultaneity being biased towards visual-leading stimulus presentation
Our experimental design is based on the idea that if audiovisual temporal integration is governed by different mechanisms as a function of leading sense, we should find dissociations with regard to asymmetries in TBW width and trainability (e.g., Powers et al, 2009) but crucially reveal absence of crossover, i.e. training one type of judgment should not transfer to the non-trained type of judgment
Summary
Most events in the environment tap into different sensory systems at the same time. For any such event, optimal integration of its multisensory properties into one coherent percept can improve perception (Sumby & Pollack, 1954; Stein & Meredith, 1993; Vroomen & de Gelder, 2000; Ramos-Estebanez et al, 2007; Kim et al, 2012; Cecere et al, 2014) and behaviour (Gielen et al, 1983; Hughes et al, 1994; Colonius & Diederich, 2004; Romei et al, 2007).Previous research has shown that temporal proximity of inputs is an important factor promoting multisensory integration (e.g., Meredith et al, 1987) and increases the likelihood that multiple sensory cues are attributed to a common external source (Welch, 1999; Spence, 2007). A great deal of research has focused on perception of audiovisual simultaneity, capitalizing on behavioural paradigms such as simultaneity judgment (SJ) and temporal order judgment (TOJ) tasks using different measures of perceived simultaneity such as the TBW as well as the point of subjective simultaneity (PSS; for a review, see Keetels & Vroomen, 2012) These studies showed that perception of simultaneity varies across a number of factors, including individual differences (Stevenson et al, 2012), developmental stages (Hillock et al, 2011), tasks/stimulus features (van Eijk et al, 2008; Stevenson & Wallace, 2013; Leone & McCourt, 2015) and attended sensory modality (Zampini et al, 2005; Spence & Parise, 2010). TBW asymmetries have been pointed out by studies investigating audiovisual binding from a developmental perspective, reporting much earlier maturation of the VA TBW than the AV TBW (e.g., Hillock et al, 2011)
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