"What Smell?" Temporarily Loading Visual Attention Induces a Prolonged Loss of Olfactory Awareness

The human sense of smell is highly sensitive, often conveying important biological signals. Yet anecdotal evidence suggests that we commonly fail to notice suprathreshold environmental olfactory stimuli. The determinants of olfactory awareness are, as yet, unknown. Here, we adapted the inattentional-blindness paradigm to test whether olfactory awareness is dependent on attention. Across three experiments, participants performed a visual search task with either a high or low perceptual load (a well-established attentional manipulation) while exposed to an ambient coffee aroma. Consistent with our hypothesis, results showed that task load modulated olfactory awareness: 42.5% fewer participants in the high- than in the low-load condition reported noticing the coffee aroma. Our final experiment demonstrates that because of unique characteristics of olfactory habituation, the consequences of inattentional anosmia can persist even once attention becomes available. These findings establish the phenomenon of inattentional anosmia and have applied implications for predicting when people may miss potentially important olfactory information.