Human temporal perception and the circadian system : effects of age, sleep pressure and light

Our intention with this work was to examine cognitive aspects of
temporal regulation in humans and delineate possible
connections to the circadian and sleep homeostatic systems.
In the first experiment reported here, we assessed cognitive
temporal orientation on the twenty-four hours scale,
operationalized here as the conscious awareness about time of
day in absence of external time cues.
We studied two age groups under conditions of both high and low
sleep pressure.
Both age groups tended to overestimate actual time of day under
both condtions, but this overestimation was more pronounced in
older participants and significantly so under conditions of
sustained wakefulness.
Under both sleep pressure conditions, both age groups displayed
a circadian oscillation in estimation errors which ran parallel
to the endogenously generated oscillation in core body
temperature.
In the younger participants, under conditions of sustained
wakefulness, this pattern was combined with an overall increase
in the magnitude of estimation errors.
Our results gave evidence that interval timing may provide a
basis for cognitive temporal orientation via a mechanism of
temporal integration.
In two further studies, we assessed interval timing in young,
healthy male participants for several stimulus magnitudes in
the seconds range using temporal production and temporal
reproduction under sustained wakefulness and controlled
multiple 75 min sleep episodes.
During temporal production conducted under controlled napping
conditions all durations were over-produced and a slight linear
increase in this behavior was observed across the protocol.
During the reproduction task under napping conditions, smaller
durations were over-reproduced but larger durations
were under-reproduced, particularly during the biological night.
During temporal production conducted under sustained
wakefulness, all durations were under-produced.
During reproduction, smaller durations were over-reproduced,
especially during the second half of the protocol.
Larger durations were under-reproduced under conditions of
sustained wakefulness.
Our findings suggest a rather weak effect of circadian phase on
interval timing and a slightly stronger effect of elevated
sleep pressure.
We also observed a large degree of inter-individual variability in
interval timing behavior which probably reflects the influence
of further variables.
Finally, we present an investigation into the effects of
differential computer screen illumination on temporal
perception.
We found that interval timing responses are typically lowered
under LED-screen illumination when compared to exposure to a
CCFL-illuminated computer screen.
In summary, we have demonstrated a possible relationship
between interval timing and cognitive temporal orientation and
were able to show that interval timing needs to be tested under
strictly controlled conditions using several methods and
stimulus durations in parallel.
Our results regarding the effects of differential screen
illumination technologies on interval timing should be of great
interest to the development of biologically and ergonomically
optimized user interfaces for information technology.