Thanks Val, but I'm still having a difficult time and I'm like a pitbull..
won't let go till I understand so forgive me for another round of this.
I understand that researchers are trying to determine if there is a built in
biological clock and to rule out environmental cues, they must be removed.
If I'm understanding correctly, whether it's constant bright light, constant
subdued light, or constant darkness, people still undergo regular changes in
physiology and sleep/awaken. However, I just don't understand how
researchers can determine how long the cycle is when they are using one of
the most powerful cues: bright light/subdued light/no light, in other words
light/dark. It seems to me this is a confounding variable and that by
manipulating light/darkness, they are manipulating and resetting the
biological clock. How valid are the results, which range from 10 to 30 hours
(average 25) and the newest results (24 hours, 11 minutes)? How are we to
ever know with certainty how long the cycle NATURALLY occurs when it is
studied in contrived situations with researchers controlling powerful light
cues?
JL Edwards
[EMAIL PROTECTED]
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> Behalf Of Val McDonald
> Sent: Tuesday, June 29, 1999 1:30 AM
> To: [EMAIL PROTECTED]
> Subject: Re: Sleep question
>
>
> I noticed your question the first time around and hoped that someone with
> more expertise than I have would answer it. Repetition drove me to trying
> to figure out the answer for myself. I'm not sure that I'm right
> about this
> so please forgive me if I err. So far as I can tell, there is
> little doubt
> that light is probably the most important synchronizer of the circadian
> rhythm. In the absence of light, changes in temperature and
> meals may also
> suffice to regulate the cycle.
>
> So long as there are REGULAR CHANGES in such things as
> temperature or light
> or REGULAR CUES (such as meals), one cannot tell if the 24 hour cycle is a
> response to environmental cues or if there is a built in biological clock.
> To determine if there is a built in biological clock, one has to
> remove the
> REGULARITIES in the environment. Accordingly, one might provide either
> continous bright light, dim light or no light. The key, I think,
> is to have
> a constant, unchanging level of illumination so that there are no cues to
> the passage of time and so that light changes will not trigger any
> physiological "biological clock" processes. Since circadian
> rhythm may also
> be regulated by changes in temperature or the presentation of meals or
> anything else that signals the passage of time, the environment has to be
> controlled to be devoid of these cues as well. I tried checking Psych
> Abstracts and, so far as I can tell, some researchers have tested
> humans in
> underground caves in conditions stripped of time cues with
> subjects left to
> control for themselves whether the light was on or off, when they ate and
> what they got (bacon and eggs could provide a hint), and what they did
> (activity vs sleep). In other experiments, the light was kept at a
> continous level.
>
> I have found this an interesting exercise in that some of what I read
> suggests that circadian rhythms for sleep can become dissociated from
> circadian rhythms for temperature. Also, one abstract reported
> considerable
> individual variations in sleep-wake cycles among subjects deprived of
> temporal cues for a month: wake cycles ranged from 10 to 30
> hours. In this
> study, subjects were asked to press a button every time they
> thought an hour
> had passed. Increases in duration of wake cycle were associated with
> increases in the amount of time experienced as an hour.
>
> Hope this helps.
>
> Val
>
> Dr. Valerye McDonald
> Professor
> Psychology Department
> University College of the Fraser Valley
> Abbotsford, B. C.,
> Canada
>
>
> -----Original Message-----
> From: JL Edwards <[EMAIL PROTECTED]>
> To: TIPS <[EMAIL PROTECTED]>
> Date: June 28, 1999 8:18 PM
> Subject: Sleep question
>
>
> >Hi ...
> >
> >I think my question may have been lost in the shuffle. I hope somone can
> >help me for I'm still struggling with the research regarding the
> circadian
> >rhythm of sleep. As I mentioned in my initial email, current researchers
> >have criticized previous research indicating that the sleep CR
> is 25 hours
> >long, basing this criticism on the fact that bright levels of light were
> >used. In fact they conclude, "Light is the most powerful synchronizer of
> the
> >biological clock." The current researchers, who are reporting a 24 rather
> 25
> >hour cycle, also used light, constantly exposing their subjects to
> "subdued"
> >levels. I don't understand how they can obtain a valid measure of the
> length
> >of CR when they also used light. Wouldn't it be better to put
> subjects in a
> >naturalistic setting where they would be exposed to natural
> light and dark
> >and have them record physiological functions, time at going to
> >sleep/awakening, etc.?
> >
> >Thanks in advance to anyone who can help me!
> >
> >JL Edwards
> >[EMAIL PROTECTED]
> >
>
>
