- Time is intimately embedded in the way that we experience the world around us. Indeed, our subjective temporal experiences seem so natural that we assume that this aspect of our conscious lives conveys something of the true nature of the world that we observe - that the events around us really do unfold in a temporally ordered and continuous way. However, deeper reflection combined with our understanding of the physics of the universe reveals a problem of subtle complexity that seems to confound any classical approach to a solution.
- Time can be addressed by its following aspects:
- Physical time: this is usually clock time; for example, time in attosecond unit can now be measured.
- Biological time: although all brain areas can be considered as biological clocks, the suprachiasmatic nucleus is the master molecular clock; it can be measured in msec units.
- Perceptual rate of time: this can be measured in cycles per second (Hz) using critical flicker frequency (CFF) psychophysical method. It varies from 300 Hz for the honeybee to 80 Hz for Buddhist monks during meditation and 60 Hz in bright light and 24 Hz in dim light for normal humans. Color fusion frequencies are lower. Time can be integrated up to 160 msec for stimuli with luminance contrast, whereas color channels have longer integration time.
- Subjective passage of time can be longer (in crisis) or shorter (with age) than physical time depending on the state of mind.
- Relative positions in time: these can be distinguished in two ways:
- Each position can be ‘earlier than’ or ‘later than’ positions. This distinction is permanent.
- Each position is either Past, Present, or Future. This distinction varies continuously.
- Time can be linear (future to present to past) or cyclic (day / night).
- There are two hypotheses for phenomenal time:
- classical psychophysical approach, which leads to temporal frequency tuned mechanisms that are not sensitive at temporal frequencies equal to or greater than CFF and
- quantum approach, where we argue that the problem of the subjective experience of time (phenomenal time) can be addressed using quantum coherence – specifically, a solitonic (traveling wave) coherent state similar to a Bose-Einstein condensate.
- In our view, both hypotheses are complementary to each other. The neural correlate of the linear nature of time includes frontal cortex and that of cyclic nature includes suprachiasmatic nucleus.
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