Evidence of perceptive impairment in OSA patients investigated by means of a visual search task

Obstructive Sleep Apnoea (OSA) is a common sleep disorder characterized by episodes of complete or partial obstruction of respiratory airways during sleep that leads to hypoxaemia and sleep fragmentation. One relevant daytime consequence of OSA is a negative impact on neurocognitive domain, ranging from psychomotor performance to executive function. In spite of a huge amount of evidence regarding cognitive impairment, little is known about perceptual processing in these patients. The aim of this research is to investigate the effects of OSA on visual mechanisms by employing a visual search paradigm. 19 OSA patients and 19 age-matched healthy controls (HC) participated in a case-control study. After a nocturnal cardiorespiratory monitoring, patients performed a visual search task in which they had to detect the presence/absence of a target (letter T) embedded in the 50% of trials into a set of distractors (letters Os, Xs, or Ls). Target's salience and distractors' numerosity were manipulated as independent variables, whereas accuracy and reaction times (RT) were recorded as dependent variables. HC, after the exclusion of any sleep disorder or sleepiness, performed the same experiments. Results generally confirmed the typical effects of visual search. OSA patients reported significantly slower RT in comparison with HC, indicating an overall perceptual deficit consisting in a harder extraction of relevant information from noise. Neither patients' age nor the objective clinical indices were associated with RT. This study indicates the presence of an impairment in OSA patients involving basic mechanisms of visual processing and likely ascribable to the disorder per se.