Chapter 13 40-Hz-Synchronicity priming of Kanizsa-figure detection demonstrated by a novel psychophysical paradigm

Recent neurophysiological studies have encouraged speculation that the synchronization of spatially distributed neuronal assemblies at around 40 Hz in the visual cortex is responsible for the binding of discrete stimulus components into coherent wholes in visual perception (e.g., Engel, König, Kreiter, & Singer, 1991; Gray, König, Engel, & Singer, 1989). There have also been a variety of experimental attempts to demonstrate a psychophysical correlate of temporal binding mechanisms during perceptual organization processes (e.g., Leonards, Singer, & Fahle, 1997; Fahle, 1993; Fahle & Koch, 1995; Kiper, Gegenfurtner, & Movshon, 1991, 1996; Blake & Yang, 1997; Usher & Donnelly, 1998). Although some of these attempts have revealed perceptual organization processes to be influenced by the temporal patterning of stimulus presentation, critically, none of these studies have produced any evidence for 40-Hz coding mechanisms consistent with neurophysiological findings (see above). Some researchers have categorically concluded from their null finding that "cortical oscillatory responses do not affect visual segmentation" (Kiper et al., 1996). In contrast, we (Elliott & Müller, 1998a, 1999a, 1999b) have developed a new experimental paradigm with which we have shown frequency-selective synchronicity priming of Kanizsa figure detection under 40-Hz presentation conditions. Under these conditions, observers are neither aware of the prime's existence, nor does the prime act as a stimulus-driven spatial-attentional cue. In this contribution, we (i) present an overview of the evidence for 40-Hz synchronicity binding based on this paradigm, (ii) consider the reasons why this paradigm has proved successful in demonstrating a 40-Hz temporal binding mechanism, and (iii) discuss the implications of our findings for the relationship between temporal binding and conscious-attentional processes.