How shall we know sleep? Since the broad adoption of polysomnography (PSG), this question is not asked often enough, and is too often answered with buoyant self-assuredness.
The scientific journey of Werner Heisenberg (Cassidy, 1992) provides some perspective on how to answer this question. Like Pavlov before him, Heisenberg was a Nobel laureate, but were that his main accomplishment, he would be lost in the oblivion of history. Pavlov achieved fame not by winning the Nobel prize for his studies of the digestive processes of dogs, but as an afterthought of that research: deriving principles of conditioning that explained the behavior of dogs and others (Windholz, 1997). Heisenberg was a German physicist, and his prize was for contributions to the theory of quantum mechanics. As part of that research program, he was frustrated in his attempts to study atomic particles because the light needed to illuminate the subject altered the path of the electrons. Thus was born Heisenberg’s Uncertainty Principle: Theact of measurement alters what one wishes to measure, rendering specific knowledge indeterminate.
Sleep scientists in the main are probably not very sympathetic to Heisenberg’s complaint. How much error could light particles have introduced to the study of electrons compared to our routine procedures? Our standard protocol is to remove individuals from their accustomedsurroundings, mount a dozen or more sets of electrodes with glue, tape, straps, clips, and the like from head to foot, and then put them to rest in an uncomfortable hospital bed. It is well established that the sleep labo-ratory setting alters sleep, as shown by disturbed sleep the first night in the laboratory (i.e., first night effect; Kales & Kales, 1984) and laboratory-home recording comparisons (Edinger et al., 1997; Stepnowsky, Moore, & Dimsdale, 2003). With the ease and confidence of a stand-up comic, the sleep technician instructs the individual to sleep naturally. Heisenberg didn’t know how good he had it.We could prove that PSG alters sleep by comparing it to a known accurate measure of sleep, but PSG is the gold standard against which other methods of sleep assessment are judged. Considering commonplace alternatives to PSG, the worthiness of actigraphy, inferring sleep from limb inactivity, or self-report (SR) sleep is evaluated by how closely they match PSG data. Of course, the matches are never perfect and assignment of fault is in part determined by convention (i.e., because PSG is objective, it is always best) and in part by philosophy of science (e.g., greater faith is assigned SR sleep in the unperturbed natural environment because it maximizes ecological validity).Perhaps we shall never know sleep, only representations of it blurred by intrusive and/or fuzzy measures. Certainly for the present, no method of measuring sleep spares the subject of our interest. The best we could aspire to is to choose a method whose profile of strengths and shortcomings seems to closely fit the circumstances and goals of a particular clinical or research evaluation. In these endeavors, we should be humbled by the implications of Heisenberg’s admonition that at all times, the relationship between sleep data and sleep is uncertain.
This epidemiological study relied on self-report (SR) data because we wanted to collect information on a large sample and using PSG or, to a lesser extent, actigraphy would have increased the survey cost enormously, would have placed a greater inconvenience burden on participants, causing greater difficulty in recruiting the desired sample, and would have dramatically extended the length of an already lengthy study due to the limited availability of assessment instrumentation.SR data have the advantages of:
|•||Being an inexpensive, convenient source of data.|
|•||Not altering the normal sleep setting.|
|•||Not altering normal sleep routines.|
|•||Being the best available measure of subjective sleep perception.|