Visual adaptation changes the susceptibility to the fission illusion.

Sound-induced flash illusion (SiFI) refers to an auditory dominance effect in which observers misperceive the number of visual flashes due to the simultaneous presentation of a different number of auditory beeps. Although the SiFI remains robust despite many factors, little is known about how the dominance of audition over vision changes as a function of spatial location in 3D space and how this corresponds with aging. In the present study, we recruited younger (18-26 years old) and older adults (60-76 years old) and presented visual stimuli in near space and auditory stimuli in far space (Vnear_Afar) or visual stimuli in far space and auditory stimuli in near space (Vfar_Anear), with the aim of exploring the effect of aging on spatial dominance in SiFI. The results showed that both participant groups exhibited a SiFI auditory dominance effect; however, older adults were more susceptible to illusions than younger adults. More importantly, for younger adults, when auditory stimuli were presented in far space, the accuracy and d' indicated that SiFI was significantly enhanced in the fission illusion, and the reaction time (RT) results showed that RT became longer in the fusion illusion. However, for older adults, the SiFI was not affected by the spatial location. Therefore, the present results reveal for the first time that the SiFI effect is modulated by the depth of auditory stimuli. Moreover, older adults were not susceptible to the depth dimension, thus showing age-related sensory decline and specifically showing a decreased ability to localize visual and auditory stimuli.

Multisensorial Perception in Chronic Migraine and the Role of Medication Overuse

The present study examined age-related differences in multisensory integration and the effect of spatial disparity on the sound-induced flash illusion—-an illusion used in previous research to assess age-related differences in multisensory integration. Prior to participation in the study, both younger and older participants demonstrated their ability to detect 1–2 visual flashes and 1–2 auditory beep presented unimodally. After passing the pre-test, participants were then presented 1–2 flashes paired with 0–2 beeps that originated from one of five speakers positioned equidistantly 100cm from the participant. One speaker was positioned directly below the screen, two speakers were positioned 50cm to the left and right from the center of the screen, and two more speakers positioned to the left and right 100cm from the center of the screen. Participants were told to report the number of flashes presented and to ignore the beeps. Both age groups showed a significant effect of the beeps on the perceived number of flashes. However, neither younger nor older individuals showed any significant effect of spatial disparity on the sound-induced flash illusion. The presence of a congruent number of beeps increased accuracy for both older and younger individuals. Reaction time data was also analyzed. As expected, older individuals showed significantly longer reaction times when compared to younger individuals. In addition, both older and younger individuals showed a significant increase in reaction time for fusion trials, where two flashes and one beep are perceived as a single flash, as compared to congruent single flash trials. This increase in reaction time was not found for fission trials, where one flash and two beeps were perceived as two flashes. This suggests that processing may differ for the two forms for fission as compared to fusion illusions.

Sound-induced flash illusion (SIFI) is an auditory-dominated multisensory integration phenomenon in which flashes presented in conjunction with an unequal number of auditory sounds are illusorily perceived as equal in number to the auditory sounds. Previous studies on the factors that impact SIFI have mainly focused on top-down and bottom-up factors. This study aimed to explore the effects of top-down cognitive expectations on the SIFI by manipulating the proportion of trial types. The results showed that the accuracy of judgment was improved and reaction times were shortened when the instructions were consistent with the actual proportion of trial type. When the instructions were not consistent with the actual proportion of trial types, the instructions could still regulate the accuracy and reaction times in judging the fission illusion (i.e., a brief flash accompanied by two auditory stimuli tends to be perceived as two flashes) regardless of the actual proportion of trial types. The results indicated that top-down cognitive expectations could significantly reduce the fission illusion and accelerate the judgment, but the effect was not significant in the fusion illusion (i.e., two brief flashes accompanied by single auditory stimuli tend to be perceived as a single flash) due to the instability of the illusion.

Multisensory integration, the ability of the brain to integrate information from different sensory modalities, is critical for responding to environmental stimuli. While older adults show changes in multisensory integration with age, the impact of allostatic load (AL) (i.e., the effect of exposure to chronic stress, which can accelerate ageing) on multisensory perception remains understudied. We explored the relationship between multisensory integration and AL in 1,358 adults aged 50+ from The Irish Longitudinal Study on Ageing by performing a Sound Induced Flash Illusion (SIFI) task at multiple audio-visual temporal asynchronies. The AL score was created using a battery of biomarkers representing the activity of four major physiological systems: immunological, cardiovascular, metabolic, and renal. The number of biomarkers for which a participant was categorised in the highest risk quartile using sex-specific cutoffs was used to produce an overall AL score. We accounted for medication use when calculating our AL score. We analysed the accuracy of illusion trials on a SIFI task using generalised logistic mixed effects regression models adjusted for a number of covariates. Observation of cross-sectional and longitudinal results revealed that lower accuracy in integration (i.e., higher SIFI susceptibility with larger temporal asynchronies) was associated with higher AL. This confirmed the distinct patterns of multisensory integration in ageing.

A single flash accompanied by two auditory beeps tends to be perceived as two flashes (Shams et al. Nature 408:788, 2000, Cogn Brain Res 14:147–152, 2002). This phenomenon is known as ‘sound-induced flash illusion.’ Previous neuroimaging studies have shown that this illusion is correlated with modulation of activity in early visual cortical areas (Arden et al. Vision Res 43(23):2469–2478, 2003; Bhattacharya et al. NeuroReport 13:1727–1730, 2002; Shams et al. NeuroReport 12(17):3849–3852, 2001, Neurosci Lett 378(2):76–81, 2005; Watkins et al. Neuroimage 31:1247–1256, 2006, Neuroimage 37:572–578, 2007; Mishra et al. J Neurosci 27(15):4120–4131, 2007). We examined how robust the illusion is by testing whether the frequency of the illusion can be reduced by providing feedback. We found that the sound-induced flash illusion was resistant to feedback training, except when the amount of monetary reward was made dependent on accuracy in performance. However, even in the latter case the participants reported that they still perceived illusory two flashes even though they correctly reported single flash. Moreover, the feedback training effect seemed to disappear once the participants were no longer provided with feedback suggesting a short-lived refinement of discrimination between illusory and physical double flashes rather than vanishing of the illusory percept. These findings indicate that the effect of sound on the perceptual representation of visual stimuli is strong and robust to feedback training, and provide further evidence against decision factors accounting for the sound-induced flash illusion.

A growing body of evidence suggests that imprecise multisensory temporal processing is associated with a range of adverse clinical outcomes. Specifically, this research has shown that the temporal binding window of audiovisual integration widens with advancing age, whereas individuals with various neurodevelopmental disorders exhibit distinctive profiles of multisensory processing when compared to their neurotypical counterparts. While this line of research has made significant inroads in emphasising the importance of multisensory processing in both typical and atypical cognition, the field would greatly benefit from the validation of web-based tools for assessing multisensory temporal processing, enabling larger sample sizes and the recruitment of typically hard-to-reach populations. Here, we assessed the reliability of a web-based version of the sound-induced flash illusion (SIFI) and examined the level of agreement between the measurements of the temporal binding window that it produces relative to those derived from the SIFI task performed under standard laboratory conditions. Our results demonstrate that both versions of the task elicit a robust SIFI effect and show a similar dependency on the stimulus onset asynchronies between the audiovisual stimuli. Furthermore, our analysis revealed strong correlations between the estimated measurements of both the width and peak amplitude of the temporal binding window derived from the online and lab-based task versions, confirming the suitability of the web-based task for assessing multisensory function. Future studies should extend the evaluation of this online implementation of the SIFI to clinical populations who exhibit impaired multisensory temporal processing, to assess its suitability for clinical research.Supplementary InformationThe online version contains supplementary material available at 10.3758/s13428-025-02791-3.

The effect of eye disease, cataract surgery and hearing aid use on multisensory integration in ageing

Sustained integration of sensory inputs over increased temporal delays is associated with reduced cognitive and physical functioning in older adults and adverse outcomes such as falls. Here, we explored the relationship between multisensory integration and a clinically relevant measure of balance/postural control; Sit-to-Stand Time, the efficiency with which an older adult can transition between a seated and a standing posture. We investigated whether temporal multisensory integration was associated with performance on the Five-Times Sit-to-Stand Test (FTSST) in a large sample of 2556 older adults (mean age = 63.62 years, SD = 7.50; 55% female) drawn from The Irish Longitudinal Study on Ageing (TILDA). K-means clustering was applied to FTSST data, yielding three clusters characterised by fast (mean = 10.88 s; n = 1122), medium (mean = 14.34 s; n = 1133) and slow (mean = 18.97 s; n = 301) sit-to-stand times. At wave 3 of TILDA, older adults participated in the Sound Induced Flash Illusion (SIFI), a measure of the precision of temporal audio–visual integration, which included three audio–visual stimulus onset asynchronies (SOAs): 70, 150 and 230 ms. Older adults with the slowest sit-to-stand times were more susceptible to the SIFI at the longest SOA (230 ms) compared to the shortest SOA (70 ms) relative to those with the fastest times (p = 0.02). Older adults who take longer to repeatedly transition from a seated to a standing posture exhibit an expanded temporal binding window for audio–visual events, supporting a link between multisensory perception and balance/postural control in ageing.

Longitudinal grip strength is associated with susceptibility to the Sound Induced Flash Illusion in older adults.

Hundreds (if not thousands) of multisensory studies provide evidence that the human brain can integrate temporally and spatially discrepant stimuli from distinct modalities into a singular event. This process of multisensory integration is usually portrayed in the scientific literature as contributing to our integrated, coherent perceptual reality. However, missing from this account is an answer to a simple question: how do confidence judgements compare between multisensory information that is integrated across multiple sources, and multisensory information that comes from a single, congruent source in the environment? In this paper, we use the sound-induced flash illusion to investigate if confidence judgements are similar across multisensory conditions when the numbers of auditory and visual events are the same, and the numbers of auditory and visual events are different. Results showed that congruent audiovisual stimuli produced higher confidence than incongruent audiovisual stimuli, even when the perceptual report was matched across the two conditions. Integrating these behavioural findings with recent neuroimaging and theoretical work, we discuss the role that prefrontal cortex may play in metacognition, multisensory causal inference and sensory source monitoring in general. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Although falling is a significant problem for older persons, little is understood about its underlying causes. Spatial cognition and balance maintenance rely on the efficient integration of information across the main senses. We investigated general multisensory efficiency in older persons with a history of falls compared to age- and sensory acuity-matched controls and younger adults using a sound-induced flash illusion. Older fallers were as susceptible to the illusion as age-matched, non-fallers or younger adults at a short delay of 70 ms between the auditory and visual stimuli. Both older adult groups were more susceptible to the illusion at longer SOAs than younger adults. However, with increasing delays between the visual and auditory stimuli, older fallers did not show a decline in the frequency at which the illusion was experienced even with delays of up to 270 ms. We argue that this relatively higher susceptibility to the illusion reflects inefficient audio-visual processing in the central nervous system and has important implications for the diagnosis and rehabilitation of falling in older persons.

Animal studies have shown that the superior colliculus (SC) is important for synthesising information from multiple senses into a unified map of space. Here, we tested whether the SC is a critical neural substrate for multisensory spatial integration in humans. To do so, we took advantage of neurophysiological findings revealing that the SC does not receive direct projections from short-wavelength-sensitive S cones. In a simple reaction-time task, participants responded more quickly to concurrent peripheral (extra-foveal) audiovisual (AV) stimuli than to an auditory or visual stimulus alone, a phenomenon known as the redundant target effect (RTE). We show that the nature of this RTE was dependent on the colour of the visual stimulus. When using purple short-wavelength stimuli, to which the SC is blind, RTE was simply explained by probability summation, indicating that the redundant auditory and visual channels are independent. Conversely, with red long-wavelength stimuli, visible to the SC, the RTE was related to nonlinear neural summation, which constitutes evidence of integration of different sensory information. We also demonstrate that when AV stimuli were presented at fixation, so that the spatial orienting component of the task was reduced, neural summation was possible regardless of stimulus colour. Together, these findings provide support for a pivotal role of the SC in mediating multisensory spatial integration in humans, when behaviour involves spatial orienting responses.

Several studies have shown that the direction in which a visual apparent motion stream moves can influence the perceived direction of an auditory apparent motion stream (an effect known as cross-modal dynamic capture). However, little is known about the role that intramodal perceptual grouping processes play in the multisensory integration of motion information. The present study was designed to investigate the time course of any modulation of the cross-modal dynamic capture effect by the nature of the perceptual grouping taking place within vision. Participants were required to judge the direction of an auditory apparent motion stream while trying to ignore visual apparent motion streams presented in a variety of different configurations. Our results demonstrate that the cross-modal dynamic capture effect was influenced more by visual perceptual grouping when the conditions for intramodal perceptual grouping were set up prior to the presentation of the audiovisual apparent motion stimuli. However, no such modulation occurred when the visual perceptual grouping manipulation was established at the same time as or after the presentation of the audiovisual stimuli. These results highlight the importance of the unimodal perceptual organization of sensory information to the manifestation of multisensory integration.

Recently, a growing number of studies have examined the role of multisensory temporal integration in people with autism spectrum disorder (ASD). Some studies have used temporal order judgments or simultaneity judgments to examine the temporal binding window, while others have employed multisensory illusions, such as the sound-induced flash illusion (SiFi). The SiFi is an illusion created by presenting two beeps along with one flash. Participants perceive two flashes if the stimulus-onset asynchrony (SOA) between the two flashes is brief. The temporal binding window can be measured by modulating the SOA between the beeps. Each of these tasks has been used to compare the temporal binding window in people with ASD and typically developing individuals; however, the results have been mixed. While temporal order and simultaneity judgment tasks have shown little temporal binding window differences between groups, studies using the SiFi have found a wider temporal binding window in ASD compared to controls. In this paper, we discuss these seemingly contradictory findings and suggest that predictive coding may be able to explain the differences between these tasks.