Effects of mood on the speed of conscious perception: behavioural and electrophysiological evidence

Abstract

When a visual stimulus is quickly followed in time by a second visual stimulus, we are normally unable to perceive it consciously. This study examined how affective states influence this temporal limit of conscious perception. Using a masked visual perception task, we found that the temporal threshold for access to consciousness is decreased in negative mood and increased in positive mood. To identify the brain mechanisms associated with this effect, we analysed brain oscillations. The mood-induced differences in perception performance were associated with differences in ongoing alpha power (around 10 Hz) before stimulus presentation. Additionally, after stimulus presentation, the better performance during negative mood was associated with enhanced global coordination of neuronal activity of theta oscillations (around 5 Hz). Thus, the effect of mood on the speed of conscious perception seems to depend on changes in oscillatory brain activity, rendering the cognitive system more or less sensitive to incoming stimuli.

Fig. 1

Stimuli and behavioural results. (a) Example of one experimental trial. After the presentation of a fixation cross, the following three visual stimuli appeared successively, centred on the same screen location: a random-letter-string mask, a number word and another mask. The presentation duration of the number word was systematically varied. Subjects were told to press one of four buttons to indicate which number-word they saw. (b) The mean percentage of correct responses is plotted for the four different target durations in each of the three mood conditions. The lines represent the psychometric Weibull functions for the three mood conditions.

Fig. 2

Alpha activity in the prestimulus interval. (a) Frequency plot of power for electrode Pz as an example. The y-axis indicates the percent change relative to the resting condition. Differences between mood conditions were most evident in the alpha frequency range. The grey bar indicates the frequency window used for statistics. (b) Scalp maps for the three mood conditions. The colour indicates the increase in alpha power. The maps show that prestimulus alpha power was lowest in negative mood, middle in neutral mood and highest in positive mood. Differences were strongest at occipital electrode sites, indicating that mood effects were largely restricted to visual processing areas.

Fig. 3

Phase synchrony during stimulus processing. (a) The difference in phase synchronization between short (mainly unseen) and long (mainly seen) target durations is plotted. The time-frequency plot shows that the strongest differences were observed in the theta frequency range (4–8 Hz). (b) The scalp map shows that significantly increased phase coupling was mainly found between occipital, parietal and frontal electrode pairs. (c) Phase-coupling for those electrode pairs that exhibited a significant difference between long and short-target durations is shown. Phase synchrony increases linearly with increasing target duration. (d) Phase synchronization in the positive, neutral and negative mood conditions is plotted for the same electrode pairs. Phase synchrony was strongest in the negative mood condition and weakest in the positive mood condition.