To uncover the neural mechanisms of stimulus perception, experimenters commonly use tasks in which subjects are repeatedly presented with a weak stimulus and instructed to report, via movement, if they perceived the stimulus. The difference in neural activity between reported stimulus (hit) and unreported stimulus (miss) trials is then seen as potentially perception-related. However, recent studies found that activity related to the report spreads throughout the brain, calling into question to what extent such tasks may be conflating activity that is perception-related with activity that is report-related. To isolate perception-related activity, we developed a paradigm in which the same mice were trained on both a regular go/no-go whisker stimulus detection task and a reversed contingencies version, in which they were trained to report the absence of a whisker stimulus. We discovered that isolated perception-related activity appears within a posterio-parietal network of cortical regions contralateral to the stimulus. This perception-related activity was on average an order of magnitude lower than the hit versus miss difference (which mostly consisted of report-related activity) and began just after the low-level stimulus response. In summary, our study revealed for the first time in mice the cortical areas that are associated specifically with the perception of a sensory stimulus and independently of the report.