Marie Holdsworth¹ (), Maëlan Q. Menétrey^1,2,3, Can Oluk¹, Michael Herzog¹; ¹Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, ²Psychophysics and Neural Dynamics Lab, Department of Radiology, Lausanne University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland, ³The Sense Innovation and Research Center, Lausanne, Switzerland

Conscious perception is preceded by long-lasting windows of unconscious processing. This is evident in the Sequential Metacontrast Paradigm (SQM), in which vernier offsets are integrated over several hundred milliseconds along a motion-stream of lines. When one line contains a vernier, all other lines are perceived as having the same offset. When the stream contains two verniers with opposite offsets, they integrate mandatorily, i.e., observers cannot distinguish the individual offsets. Previous work suggests that offsets are unconsciously summed and then read out as the conscious percept; under this model, two opposite offsets are predicted to cancel each other. Here, we aim to understand the phenomenology (or subjective experience) of the integrated percept. Using a continuous-response method (mouse adjustment), participants reported the size and direction of the perceived offset. Consistent with prior results using a two-alternative forced-choice method, participants reliably reported an offset in the single-vernier condition. In conditions with two opposite offsets, we expected an increase in the straight-line reports. However, participants reported offsets in either direction with almost equal probability, and the perceived size of these offsets was similar to that in the single-offset condition. When several offsets were shown in the same direction, participants reported larger offsets compared to single-offset conditions, in line with the model’s prediction of offset-size summation. To test the limits of these integration mechanisms, we designed another experiment in which smaller and spatiotemporally closer offsets in opposite directions were interleaved. Even then, straight-line responses did not increase, nor did the perceived offset size differ from control conditions. Overall, these findings suggest that if two offsets are in opposite directions, a winner-take-all mechanism operates and only one offset is consciously perceived. However, if offsets are in the same direction, their sizes sum. Thus, conscious perception results from a dynamic interplay between competitive and summative processes.