Sleep deprivation at the time of the field sobriety tests is significant. An inadequate amount of sleep produces tiredness and fatigued that can affect an individual’s performance on psychophysical testing. Furthermore, field sobriety tests have not been validated in people who are tired and fatigued.
Sleep deprivation/fatigue and the resultant impairment of cognitive performance and balance is discussed in the peer reviewed paper Postural Control After A Night Without Sleep by Marco Sabbri et al, which appeared in the peer reviewed Journal Neuopsychlogia in 2006 (Neuopsychlogia 44(206) 25-20-2525). “Postural control is determined by an interplay of visual, proprioceptive and vestibular inputs which are dynamically weighed to determine body position and maintain equilibrium.” According to the paper by Sabbri, it is believed that lack of sleep results in deactivation of certain brain areas concerned with mediating attention and supervision. Deactivation of these areas would be responsible for the loss of balance or postural control.