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Perception of ambiguous figures is unstable and alternates repeatedly between possible interpretations. Some approaches to explaining this phenomenon have, so far, assumed low-level bottom-up mechanisms like adaptation and mutual inhibition of underlying neural assemblies. In contrast, less precise top-down approaches assume high-level attentional control mechanisms generalised across sensory modalities. In the current work we focused on specific aspects of the top-down approach. In a first study we used dwell times (periods of transiently stable percepts) and the parameters of dwell time distribution functions to compare the dynamics of perceptual alternations between visual (Necker cube) and auditory ambiguity (verbal transformation effect). In a second study we compared the endogenous alternation dynamics of the Necker cube with parameters from two attention tasks with different regimes of temporal dynamics. The first attention task (d2) is characterised by endogenous self-paced dynamics, similar to the dynamics underlying perceptual alternations of ambiguous figures, and we found clear correlations between dwell time parameters (Necker cube) and processing speed (d2 task). The temporal dynamics of the second (go/no-go) attention task, in contrast, are exogenously governed by the stimulus protocol, and we found no statistically significant correlation with the Necker cube data. Our results indicate that both perceptual instability and higher-level attentional tasks are linked to endogenous brain dynamics on a global coordinating level beyond sensory modalities.
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INTRODUCTION: During observation of the ambiguous Necker cube, our perception suddenly reverses between two about equally possible 3D interpretations. During passive observation, perceptual reversals seem to be sudden and spontaneous. A number of theoretical approaches postulate destabilization of neural representations as a pre-condition for reversals of ambiguous figures. In the current study, we focused on possible Electroencephalogram (EEG) correlates of perceptual destabilization, that may allow prediction of an upcoming perceptual reversal. METHODS: We presented ambiguous Necker cube stimuli in an onset-paradigm and investigated the neural processes underlying endogenous reversals as compared to perceptual stability across two consecutive stimulus presentations. In a separate experimental condition, disambiguated cube variants were alternated randomly, to exogenously induce perceptual reversals. We compared the EEG immediately before and during endogenous Necker cube reversals with corresponding time windows during exogenously induced perceptual reversals of disambiguated cube variants. RESULTS: For the ambiguous Necker cube stimuli, we found the earliest differences in the EEG between reversal trials and stability trials already 1 s before a reversal occurred, at bilateral parietal electrodes. The traces remained similar until approximately 1100 ms before a perceived reversal, became maximally different at around 890 ms (p = 7.59 × 10(-6), Cohen's d = 1.35) and remained different until shortly before offset of the stimulus preceding the reversal. No such patterns were found in the case of disambiguated cube variants. DISCUSSION: The identified EEG effects may reflect destabilized states of neural representations, related to destabilized perceptual states preceding a perceptual reversal. They further indicate that spontaneous Necker cube reversals are most probably not as spontaneous as generally thought. Rather, the destabilization may occur over a longer time scale, at least 1 s before a reversal event, despite the reversal event as such being perceived as spontaneous by the viewer.
Erkunden
Eintragsart
Sprache
- Englisch (2)
Thema
- Necker cube
- Adult (1)
- ambiguous figures (1)
- Attention/*physiology (1)
- Auditory Perception/*physiology (1)
- bistability (1)
- bistable perception (1)
- EEG (1)
- Humans (1)
- perceptual reversals (1)