Is the Touch-Induced Illusory Flash Distinguishable from a Real Flash?

When the presentation of a single flash is paired with that of 2 taps, a second, illusory, flash is sometimes perceived. We presented participants with 1 or 2 flashes paired with 1 or 2 taps and asked them to report the number of flashes. In experiment 1, we used the response categories 1, 2, 3 and analyzed the responses to 2 consecutive illusory flash trials (1 flash, 2 taps). The chance to report 2 flashes was 70% when their preceding answer was 2 and only 10% when it was 1 (p < .001). This effect can occur when participants' percept neither fits the 1 or 2 response category. In experiment 2, we introduced a new response category, viz. 'something different from 1 or 2 flashes' and found that observers used this category in 50.0% of the illusory flash trials, while 2 real flashes were reported as 2 in 87.3% of the trials (χ2 = 116.62; p < .001). We conclude that the percept of an illusory flash differs from that of a real flash.