When two objects move randomly across a screen and occasionally change direction, brief beeps synchronized with the direction changes of one object increase its perceived speed relative to the other. This so-called beep-speed illusion has been demonstrated in two-alternative forced-choice tasks, in which participants choose which of two objects appears to move faster. A common critique is that differences in perceived speed may not reflect conscious visual experience but could arise from response biases.

In the present study (N = 65), we tested this possibility by comparing the beep-speed illusion across two paradigms: a two-alternative forced-choice task and an equality-judgment task. In both tasks, participants viewed two moving objects. One object always moved at 4.5 degrees of visual angle per second, with direction changes synchronized with brief beeps. The speed of the other object varied across trials from 2 to 7 degrees per second.

In the two-alternative forced-choice task, participants indicated which object they perceived as moving faster. We fitted a psychometric function to these responses and extracted the point of subjective equality as an index of the magnitude of the beep-speed illusion. In the equality-judgment task, participants reported whether the objects appeared to move at the same or different speeds. For these responses, we fitted a normal distribution and estimated the shift of its center as an index of the illusion’s magnitude.

We observed the beep-speed illusion at a similar magnitude of 4–5% in both tasks, ruling out the alternative interpretation that it arises without entering visual awareness.