Chemical sensory stimuli are omnipresent in everyday life as well as during work. Very low levels of environmental chemicals can be detected and categorized as pleasant or unpleasant. Influences of odors on both human behavior and mental performance are phenomena that are generally accepted, despite the paucity of scientific proof. Investigations about odor effects on mental performance have mostly failed to show any direct effects. In a study with 5-year-old children (Epple & Herz, 1999), performance on a cognitive test in rooms with odors was similar to that in rooms without odors. However, the study showed that odors can become conditioned to experimental states and can have influences on behavior. Gilbert, Knasko, and Sabini (1997) tested the effect of ambient room-odor conditions on performance and mood and found no influence of odor conditions; odor suggestion, however, produced a significant sex-related interaction on a digit deletion task, irrespective of actual ambient odor presence.
Only Degel and Koster (1999) have shown that a room odorized with lavender had a positive effect on task performance and that one odorized with jasmine negatively affected performance. The arousal optimum concept (Yerkes-Dodson law; Yerkes & Dodson, 1908) was applied by Degel and Koster to explain why the arousing odor impaired performance whereas the more sedative odor facilitated performance. Only Knasko (1993) has investigated the effect of intermittent bursts of pleasant and unpleasant odors on task performance. No effects on performance were found, but participants who had been exposed to the malodors reported retrospectively that they thought the odors had a negative effect on task performance, mood, and perceived health. Neither of these studies evaluated physiological parameters.
Two main lines of arguments are found concerning performance decrements under environmental stimuli: One argues that such stimuli lead to an increase in arousal (activation) above an optimum, the other that such stimuli cause withdrawal of attention (Hockey 1997; Loeb, 1986). The arousal concept, which may be traced back to Sharpless and Jasper (1956), assumes that activation or arousal is dependent on the level of sensory input as well as the level of ongoing activity and that there is an optimum level of arousal below or above which performance will be inferior (Yerkes-Dodson law; Yerkes & Dodson, 1908). The distraction hypothesis holds that extraneous stimuli may elicit responses incompatible with task performance and so degrade it. Broadbent (1979) assumed that continuous, nonnovel stimuli will rail to distract. Therefore distraction relies on stimulus novelty or on a change of stimulation, whereas arousal increase above an optimum is more applicable to continuous stimulation.
In psychophysiological terms, moderate novel stimuli may induce an orienting response. Based on Sokolov (1963) and Lacey (1967), the orienting reflex is assumed to functionally influence perceptual thresholds in facilitating the processing of information about the external environment; it is therefore most plausible that stimuli that induce an orienting response have the potency to impair performance (Filion, Dawson, Schell, & Hazlett, 1991).
The conventional interpretation of Pavlov (1927) and Sokolov (1963) suggests that any perceived change in stimulation is sufficient to produce an orienting response, but this seems implausible in light of the great variability of the natural environment (Ben-Shakhar, Gati, Bassat, & Sniper, 2000). Bernstein (1969), Maltzman (1977), and Naatanen (1997) argued that a change in stimulus input may not be sufficient to induce an orienting response and proposed stimulus significance as an additional condition for the response. Gati and Ben-Shakhar (1990) assumed that both stimulus input and stimulus representations can be characterized by sets of features and that the assessment of each factor is carried out by a separate feature-matching process. …