Under special conditions an asymmetric interaction has been reported between different aspects of face perception: irrelevant variations in facial expression or facial speech do not influence reaction times in a face identity task, while irrelevant variations in facial identity do influence performance in a facial expression classification task [106].
In an oddball paradigm, task-irrelevant changes in facial expression, i.e. fearful and happy deviants, elicited differential ERPs relative to neutral standard expressions in three analysis windows.
It has been suggested that internal structures of the skull are irrelevant to the visible facial symmetry, i.e., the midline of the cranial base can deviate from the visible facial symmetry [ 15].
This supports the suggestion that internal structures of the skull may be irrelevant to the visible facial symmetry, even in symmetric skulls.
Using a go/no go task with positive, negative, and neutral facial expressions (task irrelevant stimulation), Hilimire et al. [ 8] found pronounced early negativity at occipital sites and positivity at frontocentral sites to positive emotions in older adults.
Interestingly, there is evidence that brain activation in response to threatening faces in SAD patients differs greatly from the activation in HCs when facial emotional expressions are task irrelevant, which suggests an automatic processing of facial anger cues in SAD patients [ 10].
Its implication has been demonstrated in the perception of task-irrelevant fearful faces [52] and in non-conscious facial expression perception [53], but its role remains debated.
To minimize task effects related to facial or emotional processing, facial stimuli were irrelevant to a primary task of learning associative pairings between a subsequently presented visual character and a spoken word.
In addition, face regions themselves can have irrelevant information due to intra-class variability such as occlusions, facial expressions, illumination changes, and pose changes.
