Task requirements affect the neural correlates of consciousness

Abstract

In the search for the neural correlates of consciousness, it is often assumed that there is a stable set within the relevant sensory modality. Within the visual modality, the debate has centred upon whether frontal or occipital activations are the best predictors of perceptual awareness. Although not accepted by all as definitive evidence, no-report and decoding studies have indicated that occipital activity is the most consistently correlated with perceptual awareness whereas frontal activity might be closely related to aspects of cognition typically related to reports. However, perception is rarely just passive perception of something, but more or less always perception for something. That is, the task at hand for the perceiver may influence what is being perceived. This suggests an alternative view: that consciousness is not one specific 'function' that can be localized consistently to one area or event-related component and that the specific attributes of the neural correlates of consciousness depend on the task at hand. To investigate whether and how tasks may influence the neural correlates of consciousness, we here contrasted two tasks, a perceptual task and a conceptual task, using identical stimuli in both tasks. Using magnetoencephalography, we found that the perceptual task recruited more occipital resources than the conceptual task. Furthermore, we found that between the two conditions, the amount of frontal resources recruited differed between different gradations of perceptual awareness partly in an unexpected manner. These findings support a view of task affecting the neural correlates of consciousness.

Keywords: consciousness; magnetoencephalography; perception; vision.

FIGURE 1

Paradigm: A fixation cross was presented for 1000 ms, followed by a delay of 1000 ms, to prevent forward masking of the target stimulus. A pair of letters was then presented for 33 ms immediately followed by a mask that remained on until the participant indicated whether the two letters were ‘same’ or ‘different’. In the perceptual task, the target letters were defined as ‘same’ if they were identical, for example, ‘RR’, and ‘different’ in all other cases. For the conceptual task, the target letters were defined as ‘same’ if they were of the same type according to whether they were consonants or vowels, for example, ‘EU’ or ‘SV’, and ‘different’ if they were of opposite types, for example, ‘EV’. After that, participants had to indicate perceptual experience by one of four ratings, no experience, weak glimpse, almost clear experience or clear experience.

FIGURE 2

Behavioural performance. (a) Accuracy for each of the PAS ratings per task. Error bars are 95% confidence intervals. (b) Response times for each of the PAS ratings per task. Error bars are 95% confidence intervals.

FIGURE 3

Collapsed activations—grand average. (a) Grand average over sensors for the collapsed activation. (b) An early activation (250 ms) is seen over the lateral occipital cortex and (c) a late activation (540 ms) over the medial orbitofrontal cortex. (d) Time courses for the indicated regions. The mean over all sources within the region was found for each time point. On the participant level, trials were averaged across all PAS ratings, and subsequently, a grand average across participants was done irrespective of task. The lateral occipital cortex and the medial orbitofrontal cortex were defined using the Desikan–Killiany atlas as implemented in freesurfer (Desikan et al., 2006).

FIGURE 4

Estimated main effects and tested interactions. (a) Number of trials per participant and how many participant data sets survived the cut‐off (minimum 20 trials) per PAS rating. (b) Estimated means of activity in the two labels and their associated standard errors. (c) The estimated interaction effect for the lateral occipital area over the early range (100–400 ms). (d) The estimated interaction effect for the medial orbitofrontal cortex over the late range (400–700 ms)