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Anesthetic-induced changes in the neural activity of the brain have been recently utilized as a research model to investigate the neural mechanisms of phenomenal consciousness. However, the anesthesiologic definition of consciousness as ‘‘responsiveness to the environment’’ seems to sidestep the possibility that an unresponsive individual may have subjective experiences. The aim of the present study was to analyze subjective reports in sessions where sedation and the loss of responsiveness were induced by dexmedetomidine, propofol, sevoflurane or xenon in a nonsurgical experimental setting. After regaining responsiveness, participants recalled subjective experiences in almost 60% of sessions. During dexmedetomidine sessions, subjective experiences were associated with shallower ‘‘depth of sedation’’ as measured by an electroencephalography-derived anesthesia depth monitor. Results confirm that subjective experiences may occur during clinically defined unresponsiveness, and that studies aiming to investigate phenomenal consciousness under sedative and anesthetic effects should control the subjective state of unresponsive participants with post-recovery interviews.

To examine the neural correlates and timing of human visual awareness, we recorded event-related potentials (ERPs) in two experiments while the observers were detecting a grey dot that was presented near subjective threshold. ERPs were averaged for conscious detections of the stimulus (hits) and nondetections (misses) separately. Our results revealed that hits, as compared to misses, showed a negativity around 180-350 ms at occipital and posterior temporal sites. It was followed by a positive wave after 400-500 ms, peaking at parietal sites. These correlates were not affected by a manipulation of attention. The early negativity, called 'visual awareness negativity' (VAN), may be a general, primary electrophysiological correlate of visual awareness. The present data show that it can be observed in response to appearance of a stimulus in visual awareness and that it generalizes across different manipulations of stimulus visibility.

Earlier studies suggest that interhemispheric processing increases the processing power of the brain in cognitively complex tasks as it allows the brain to divide the processing load between the hemispheres. We report two experiments suggesting that this finding does not generalize to word–picture pairs: they are processed at least as efficiently when processed by a single hemisphere as compared to processing occurring between the two hemispheres. We examined whether dividing the stimuli between the visual fields/hemispheres would be more advantageous than unilateral stimulus displays in the semantic categorization of simultaneously presented pictures, words, and word–picture pairs. The results revealed that within-domain stimuli (semantically related picture pairs or word pairs) were categorized faster in bilateral than in unilateral displays, whereas cross-domain stimuli (word–picture pairs) were not categorized faster in bilateral than in unilateral displays. It is suggested that interhemispheric sharing of word–picture stimuli is not advantageous as compared to unilateral processing conditions because words and pictures use different access routes, and therefore, it may be possible to process in parallel simultaneously displayed word–picture stimuli within a single hemisphere.

In this study, we criticize the notion of bradyphrenia and argue that "slowness of thought" in Parkinson"s disease (PD) must be analyzed as slowness of different information-processing stages and that unselected patients should not be used in experimental studies. We selected 32 patients with a long history of PD and 50 control subjects. Sixteen patients had mild cognitive deterioration (not dementia) and 16 patients had preserved cognitive capacities; otherwise the groups were matched. By using computerized tests, we investigated three separate stages: automatic and controlled processing and motor programming. The results indicate that patients with mild cognitive deterioration are slower than patients with preserved cognitive capacities or controls in automatic visual and in controlled processing but not in motor programming. We conclude that the slowing of controlled processing reflects the disruption of central neural networks, that a long history of PD does not necessitate cognitive slowing, and that PD is not a neuropsychologically serviceable category.

Ambiguous (or bistable) figures are visual stimuli that have two mutually exclusive perceptual interpretations that spontaneously alternate with each other. Perceptual reversals, as compared with non-reversals, typically elicit a negative difference called reversal negativity (RN), peaking around 250 ms from stimulus onset. The cognitive interpretation of RN remains unclear: it may reflect either bottom-up processes, attentional processes that select between the alternative views of the stimulus, or it may reflect the change in the contents of subjective awareness. In the present study, event-related potentials in response to endogenous unilateral and bilateral reversals of two Necker lattices were compared with exogenously induced reversals of unambiguous lattices. The RN neither resembled the attention-related N2pc response, nor did it correlate with the content of subjective visual awareness. Thus, we conclude that RN is a non-attentional ERP correlate of the changes in the perceptual configuration of the presented object.