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Stimulus requirements for face perception: an analysis based on "totem poles".

Paras CL, Webster MA - Front Psychol (2013)

Bottom Line: This allowed us to examine the prominence and properties of different features and their necessary configurations.Moreover, the prominence of eyes depended primarily on their luminance contrast and showed little influence of chromatic contrast.This suggests that the requisite trigger features are sufficient to holistically "capture" the surrounding noise structure to form the facial representation.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, University of Nevada Reno, NV, USA.

ABSTRACT
The stimulus requirements for perceiving a face are not well defined but are presumably simple, for vivid faces can often by seen in random or natural images such as cloud or rock formations. To characterize these requirements, we measured where observers reported the impression of faces in images defined by symmetric 1/f noise. This allowed us to examine the prominence and properties of different features and their necessary configurations. In these stimuli many faces can be perceived along the vertical midline, and appear stacked at multiple scales, reminiscent of "totem poles." In addition to symmetry, the faces in noise are invariably upright and thus reveal the inversion effects that are thought to be a defining property of configural face processing. To a large extent, seeing a face required seeing eyes, and these were largely restricted to dark regions in the images. Other features were more subordinate and showed relatively little bias in polarity. Moreover, the prominence of eyes depended primarily on their luminance contrast and showed little influence of chromatic contrast. Notably, most faces were rated as clearly defined with highly distinctive attributes, suggesting that once an image area is coded as a face it is perceptually completed consistent with this interpretation. This suggests that the requisite trigger features are sufficient to holistically "capture" the surrounding noise structure to form the facial representation. Yet despite these well articulated percepts, we show in further experiments that while a pair of dark spots added to noise images appears face-like, these impressions fail to elicit other signatures of face processing, and in particular, fail to elicit an N170 or fixation patterns typical for images of actual faces. These results suggest that very simple stimulus configurations are sufficient to invoke many aspects of holistic and configural face perception while nevertheless failing to fully engage the neural machinery of face coding, implying that that different signatures of face processing may have different stimulus requirements.

No MeSH data available.


Related in: MedlinePlus

Ratio of the average luminance (pixel gray level) of features relative to the average luminance of the surrounding annulus.
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Figure 3: Ratio of the average luminance (pixel gray level) of features relative to the average luminance of the surrounding annulus.

Mentions: Table 2 lists for eight observers the percentage of time that a particular feature in the face was reported. Eyes were by far the most prominent percept, averaging 95% and close to 100% for individual observers. These were followed by a nose or mouth, which were indentified much less consistently across observers (60–70% of the time). Finally, ears were identified by only two of the eight observers. Thus a pair of eyes, perhaps combined with either a nose or a mouth, appeared to be critical for eliciting a face percept. Moreover, the regions identified as eyes were strongly biased toward lower luminances (pixel values) than the local surround, or in other words to darker spots in the images (Figure 3). In contrast, there was not a significant bias in the luminance polarity of either the mouth or the nose. Again, this polarity was assessed by comparing the average pixel level within an elliptical region fit to the observer’s demarcation of the feature, relative to the average level measured within a surrounding annulus, and thus probably failed to capture the relevant levels in some faces, for example when the eyes were elicited by an outline or higher luminance variance rather than a uniform area. Nevertheless, the results suggest that in order to perceive a face, the image had to contain dark spots for the eyes, while the mouth or nose was defined by its spatial information but not by its contrast.


Stimulus requirements for face perception: an analysis based on "totem poles".

Paras CL, Webster MA - Front Psychol (2013)

Ratio of the average luminance (pixel gray level) of features relative to the average luminance of the surrounding annulus.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3569666&req=5

Figure 3: Ratio of the average luminance (pixel gray level) of features relative to the average luminance of the surrounding annulus.
Mentions: Table 2 lists for eight observers the percentage of time that a particular feature in the face was reported. Eyes were by far the most prominent percept, averaging 95% and close to 100% for individual observers. These were followed by a nose or mouth, which were indentified much less consistently across observers (60–70% of the time). Finally, ears were identified by only two of the eight observers. Thus a pair of eyes, perhaps combined with either a nose or a mouth, appeared to be critical for eliciting a face percept. Moreover, the regions identified as eyes were strongly biased toward lower luminances (pixel values) than the local surround, or in other words to darker spots in the images (Figure 3). In contrast, there was not a significant bias in the luminance polarity of either the mouth or the nose. Again, this polarity was assessed by comparing the average pixel level within an elliptical region fit to the observer’s demarcation of the feature, relative to the average level measured within a surrounding annulus, and thus probably failed to capture the relevant levels in some faces, for example when the eyes were elicited by an outline or higher luminance variance rather than a uniform area. Nevertheless, the results suggest that in order to perceive a face, the image had to contain dark spots for the eyes, while the mouth or nose was defined by its spatial information but not by its contrast.

Bottom Line: This allowed us to examine the prominence and properties of different features and their necessary configurations.Moreover, the prominence of eyes depended primarily on their luminance contrast and showed little influence of chromatic contrast.This suggests that the requisite trigger features are sufficient to holistically "capture" the surrounding noise structure to form the facial representation.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, University of Nevada Reno, NV, USA.

ABSTRACT
The stimulus requirements for perceiving a face are not well defined but are presumably simple, for vivid faces can often by seen in random or natural images such as cloud or rock formations. To characterize these requirements, we measured where observers reported the impression of faces in images defined by symmetric 1/f noise. This allowed us to examine the prominence and properties of different features and their necessary configurations. In these stimuli many faces can be perceived along the vertical midline, and appear stacked at multiple scales, reminiscent of "totem poles." In addition to symmetry, the faces in noise are invariably upright and thus reveal the inversion effects that are thought to be a defining property of configural face processing. To a large extent, seeing a face required seeing eyes, and these were largely restricted to dark regions in the images. Other features were more subordinate and showed relatively little bias in polarity. Moreover, the prominence of eyes depended primarily on their luminance contrast and showed little influence of chromatic contrast. Notably, most faces were rated as clearly defined with highly distinctive attributes, suggesting that once an image area is coded as a face it is perceptually completed consistent with this interpretation. This suggests that the requisite trigger features are sufficient to holistically "capture" the surrounding noise structure to form the facial representation. Yet despite these well articulated percepts, we show in further experiments that while a pair of dark spots added to noise images appears face-like, these impressions fail to elicit other signatures of face processing, and in particular, fail to elicit an N170 or fixation patterns typical for images of actual faces. These results suggest that very simple stimulus configurations are sufficient to invoke many aspects of holistic and configural face perception while nevertheless failing to fully engage the neural machinery of face coding, implying that that different signatures of face processing may have different stimulus requirements.

No MeSH data available.


Related in: MedlinePlus