Reversing the Luminance Polarity of Control Faces: Why Are Some Negative Faces Harder to Recognize, but Easier to See?

Abstract

Control stimuli are key for understanding the extent to which face processing relies on holistic processing, and affective evaluation versus the encoding of low-level image properties. Luminance polarity (LP) reversal combined with face inversion is a popular tool for severely disrupting the recognition of face controls. However, recent findings demonstrate visibility-recognition trade-offs for LP-reversed faces, where these face controls sometimes appear more salient despite being harder to recognize. The present report brings together findings from image analysis, simple stimuli, and behavioral data for facial recognition and visibility, in an attempt to disentangle instances where LP-reversed control faces are associated with a performance bias in terms of their perceived salience. These findings have important implications for studies of subjective face appearance, and highlight that future research must be aware of behavioral artifacts due to the possibility of trade-off effects.

Saccadic eye movements are deployed faster for salient facial stimuli, but are relatively indifferent to their emotional content

“…Upright (luminance retained) faces did, however, receive faster saccadic response times when faces were low-and high-frequency-filtered, but this was influenced by the use of contrast normalisation, where detectability advantages for upright low frequency faces relied on their consistency in terms of apparent, perceived contrast, while detectability advances for high frequency faces relied on naturally-occurring contrast differences between expressions. These findings are consistent with previous literature, in that they demonstrate an unclear interaction between contrast, luminance, and orientation for facial emotion processing [23,26], and contribute to recent literature regarding the role of luminance polarity reversal, showing that reflexive eye movements are not facilitated by an increase of local dark regions [29,34]…”

“…In the present study, saccadic response times did not differ according to the format of typical, broadband facial stimuli, such that the combination of spatial inversion and luminance polarity reversal did not influence their detectability. This finding is surprising, because it suggests that saccadic latency is indifferent to the holistic information present in upright faces; an unexpected outcome given the renowned face inversion effect that is consistently observed for regular, unfiltered faces [29,33]. Upright (luminance retained) faces did, however, receive faster saccadic response times when faces were low-and high-frequency-filtered, but this was influenced by the use of contrast normalisation, where detectability advantages for upright low frequency faces relied on their consistency in terms of apparent, perceived contrast, while detectability advances for high frequency faces relied on naturally-occurring contrast differences between expressions.…”

“…Finally, faces were presented in one of two ways: in their natural, upright format, and in a manipulated format in which they were rotated 180 • and subjected to luminance polarity reversal. This method for creating control faces significantly disrupts facial emotion recognition while preserving low-level image properties including spatial frequency and contrast associated with the original, natural format of faces [22,29].…”

“…There are also mixed findings regarding the effect of luminance polarity reversal on the salience of faces, where some evidence implies that the increase in darker local regions enhances stimulus visibility [29]. Saccadic latency, as a measure of stimulus salience, is therefore a good candidate technique for further exploring the effect of luminance polarity reversal on face localisation.…”

“…The present study created control versions of facial stimuli using spatial inversion combined with luminance polarity reversal, a combined treatment known to significantly impede facial recognition [22]. Recently, however, some evidence suggests that luminance polarity reversal may, in some cases, inadvertently increase the perceived salience of a control face (for review, see [29]. Saccadic latency is therefore an ideal candidate for exploring these effects, particularly because findings regarding the effects of holistic information in upright versus inverted faces for saccadic responses are fairly mixed.…”