Neural oscillations, excitability and perceptual decisions

Numerous studies have demonstrated that the power of ongoing alpha oscillations in the EEG is inversely related to neural excitability, as reflected in spike-firing rate, multi-unit activity, or the hemodynamic fMRI signal. Furthermore, alpha oscillations also affect behavioral performance in perceptual tasks. However, it is surprisingly unclear which latent perceptual or cognitive mechanisms mediate this effect. For example, an open question is whether neuronal excitability fluctuations induced by alpha oscillations affect an observer’s acuity or perceptual bias. I will present a series of experiments that aim to clarify the link between oscillatory power and perceptual performance. In short, these experiments indicate that performance during moments of weak pre-stimulus power, indicating greater excitability, is best described by a more liberal detection criterion rather than a change in detection sensitivity or discrimination accuracy. This result brings up a thorny question: do pre-stimulus oscillations have any effect on observers’ sensory experience at all, or do they affect observers’ strategic decision making? I will argue that this effect is due to an amplification of both sensory signal and noise, and that this amplification occurs already during the first stages of visual processing.