In the original double flash illusion, a visual flash (e.g., a sharp-edged disk, or uniformly filled circle) presented with two short auditory tones (beeps) is often followed by an illusory flash. The illusory flash has been previously shown to be triggered by the second auditory beep. The current study extends the double flash illusion by showing that this paradigm can not only create the illusory repeat of an on-off flash, but also trigger an illusory expansion (and in some cases a subsequent contraction) that is induced by the flash of a circular brightness gradient (gradient disk) to replay as well. The perception of the dynamic double flash illusion further supports the interpretation of the illusory flash (in the double flash illusion) as similar in its spatial and temporal properties to the perception of the real visual flash, likely by replicating the neural processes underlying the illusory expansion of the real flash. We show further that if a gradient disk (generating an illusory expansion) and a sharp-edged disk are presented simultaneously side by side with two sequential beeps, often only one visual stimulus or the other will be perceived to double flash. This indicates selectivity in auditory–visual binding, suggesting the usefulness of this paradigm as a psychophysical tool for investigating crossmodal binding phenomena.
In an earlier study, we demonstrated that the temporal rate adaptation effect can be transferred from audition to vision and vice versa. However, it was unclear whether this effect was due to a top-down cognitive process, or rather to an earlier calibration process which is stimulus-driven and automatic. We therefore examined the effect of interocular masking of the adapting stimuli on the temporal rate adaptation and its cross-modal transfer from vision to audition (VA). Participants were trained, using feedback, to classify repetitive auditory stimuli presented at a range of frequencies (3.25–4.75 Hz) as fast or slow (as compared to the average frequency of 4 Hz). Afterwards, subjects were repeatedly exposed to visual stimuli at a specific rate (3 or 5 Hz). This adaptation stimulus was masked by continuous flash suppression (CFS). During CFS, a stimulus presented to one eye can be suppressed from awareness by a stream of constantly changing images in the other eye. To test whether adaptation resulted from this less visible exposure, participants then performed the same task as in the training, but without feedback. Test and adaptation tasks were presented in 20 alternating blocks. A comparison of the pre- and post-adaptation responses showed cross-modal changes in subjects’ perception of temporal rate. Adaptation to the masked 5 Hz (3 Hz) stimuli led to subsequent stimuli seeming slower (faster) than they had before adaptation. Since the adaptation stimuli were mostly masked by CFS, the results suggest that temporal rate adaptation and its cross-modal transfer occur mostly at a subconscious level.
We previously reported our discovery that temporal rate adaptation transfers bidirectionally between vision and audition. Temporal frequency channels are linked across audition and vision (Yao et al., 2009); but duration channels for audition and vision are thought to be independent (Heron et al., 2012). We used our paradigm to characterize linkages between auditory and visual channels by measuring whether or not transfer of adaptation still occurs as the discrepancy between adaptation and test frequencies increases. Participants ran in three experimental sessions, each with a different adaptation frequency. They were trained, using feedback, to classify flickering visual stimuli (ranging in frequency from 3.25–4.75 Hz) as fast or slow (relative to 4 Hz). They then classified 140 pre-adaptation test trials with feedback, providing a baseline. Afterwards, 30 adaptation trials of auditory stimuli beeping at either 5, 8, or 12 Hz were presented, followed by 20 alternating blocks of 7 adaptation and 7 post-adaptation test trials (without feedback). We compared the PSE of the pre- and post-adaptation trials to quantify the cross-modal transfer and found that the aftereffect occurred when the adaptation frequency was most similar to the test frequencies but was no longer present with larger discrepancies. These results rule out response bias as a plausible explanation for our original findings and suggest that the timing mechanisms underlying rate perception are consistent with supramodal channels that are tuned.