This is the accepted version of the paper.This version of the publication may differ from the final published version. Copyright and reuse: City Research Online aims to make research outputs of City, University of London available to a wider audience. Copyright and Moral Rights remain with the author(s) and/or copyright holders. URLs from City Research Online may be freely distributed and linked to. City Research Online: http://openaccess.city.ac.uk/ publications@city.ac.uk Permanent repository link: City Research OnlineThe APA has copyright on this article. When published, it can be found at: improvements can be predicted quantitatively, assuming estimates are combined by summation, a process described as optimal when summation is weighted in accordance with the variance associated with each of the initially independent estimates. We assessed this possibility for visual and tactile information regarding temporal intervals. In Experiment 1, 12 musicians and 12 nonmusicians judged durations of 300 and 600 ms, compared to test values spanning these standards.Bimodal precision increased relative to unimodal conditions, but not by the extent predicted by optimally weighted summation. In Experiment 2, six musicians and six other participants each judged six standards, ranging from 100 ms to 600 ms, with conflicting cues providing a measure of the weight assigned to each sensory modality. A weighted integration model best fitted these data, with musicians more likely to select near-optimal weights than non-musicians. Overall, data were consistent with the existence of separate visual and tactile clock components at either the counter/integrator or memory stages. Independent estimates are passed to a decisional process, but not always combined in a statistically optimal fashion. Statement of public significanceWe are able to judge the duration of events as they unfold (e.g. the time for which somebody holds our gaze). Sometimes, this information is conveyed to several of our senses at once (e.g. both seeing and feeling the duration of a caress). Theorists argue about whether time intervals are calculated separately for each sense, or rely on a common centralised timer. This study suggests that when people experience the duration of events via both vision and touch, they gain a multisensory benefit, performing better than when they receive just visual or just tactile stimulation.This kind of benefit can only accrue if time is first estimated independently within each sense, suggesting that separate timers exist.Humans and other animals express their ability to time intervals through a wide variety of behaviours. In the lab, this ability is often assessed by requiring experimental participants to make judgments about the duration of events. However, our knowledge regarding the neurocognitive bases of these judgments remains hazy. One debate concerns the centralised versus distributed nature of the hypothetical internal clock or clocks (Ivry & Schlerf, 2008;Ivry & Spencer, 2004 Revina, Bruno, & Johnston, 2012;and Morgan...

Some people experience auditory sensations when seeing visual flashes or movements. This prevalent synaesthesia-like visually evoked auditory response (vEAR) could result either from overexuberant cross-activation between brain areas and/or reduced inhibition of normally occurring cross-activation. We have used transcranial alternating current stimulation (tACS) to test these theories. We applied tACS at 10 Hz (alpha band frequency) or 40 Hz (gamma band), bilaterally either to temporal or occipital sites, while measuring same/different discrimination of paired auditory (A) versus visual (V) Morse code sequences. At debriefing, participants were classified as vEAR or non-vEAR, depending on whether they reported “hearing” the silent flashes. In non-vEAR participants, temporal 10-Hz tACS caused impairment of A performance, which correlated with improved V; conversely under occipital tACS, poorer V performance correlated with improved A. This reciprocal pattern suggests that sensory cortices are normally mutually inhibitory and that alpha-frequency tACS may bias the balance of competition between them. vEAR participants showed no tACS effects, consistent with reduced inhibition, or enhanced cooperation between modalities. In addition, temporal 40-Hz tACS impaired V performance, specifically in individuals who showed a performance advantage for V (relative to A). Gamma-frequency tACS may therefore modulate the ability of these individuals to benefit from recoding flashes into the auditory modality, possibly by disrupting cross-activation of auditory areas by visual stimulation. Our results support both theories, suggesting that vEAR may depend on disinhibition of normally occurring sensory cross-activation, which may be expressed more strongly in some individuals. Furthermore, endogenous alpha- and gamma-frequency oscillations may function respectively to inhibit or promote this cross-activation.