Measuring conscious tactile perception without report: pupil, blink, and microsaccade signatures of a tactile no-report paradigm
Conscious perception is often inferred from behavioral reports, which conflate awareness-related neural signals with the motor and decision processes required to respond. No-report paradigms address this by using spontaneous physiological signals, such as eye movements, to infer perception. Although our group developed a no-report visual paradigm, we had not applied this approach to touch. We developed a no-report tactile paradigm using the Galileo stimulation system to deliver pneumatic air puffs to non-thumb fingers on both hands while tracking eye movements. Participants reported sensations from the Report hand while receiving threshold-level puffs on both hands; eye metrics were used to infer perception in the No-Report hand. Perceived threshold-level stimuli elicited greater pupil dilation and more post-stimulus blinking than identical unperceived stimuli, with effects lasting 1 - 2 seconds. Microsaccade rate decreased after stimulus onset, but this suppression did not reach statistical significance. A stacked support vector machine trained on the Report eye-tracking measures was applied to classify No-Report trials and successfully separated [Predicted] Perceived from [Predicted] Not Perceived trials (AUC = .92; cross-validated accuracy = 72%; sensitivity = 90% at 80% specificity; label-permutation p < .001). These findings show that eye tracking can detect conscious tactile perception without overt responses and offer a noninvasive, scalable approach for studying tactile perception in patients with self-reported disabilities, including comatose or intubated patients.