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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

Examples of the faces reported by observers. After identifying and describing the face, observers drew on the image to indicate the perceived position and shape of features. Different features were coded with different colors (e.g., red for eyes, blue for nose, etc.) so that their dimensions could be analyzed afterward.
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Figure 2: Examples of the faces reported by observers. After identifying and describing the face, observers drew on the image to indicate the perceived position and shape of features. Different features were coded with different colors (e.g., red for eyes, blue for nose, etc.) so that their dimensions could be analyzed afterward.

Mentions: After completing this labeling, the observers next identified the visible features of the face from a menu that included eyes, nose, mouth, ears, eyebrows, and head outline. For each they used a graphics pad to point to the center of the relevant feature, whose coordinates were then recorded, and also used a drop-down menu to record the distinctiveness of the feature. Finally, they next used the graphics pad to outline or fill in the contours of each feature by drawing on the image. These drawings were stored by overwriting the pixel values in a copy of the image, using different colors for each chosen feature so that these could be distinguished for subsequent analysis. Examples of faces drawn by the observers (who varied widely in artistic talent) are illustrated in Figure 2. Once these steps were completed the original image was redisplayed so that observers could look for additional faces. Typically many faces were detected in a single image. When observers felt they could no longer find new ones, they advanced to the next image, and repeated the sequence of responses. Images were shown in random order both within and across subjects. The drawings were analyzed by fitting ellipses to each selected feature to estimate the position, orientation, and aspect ratio of the smallest ellipse that encompassed 95% of the chosen pixels. The luminance contrast of the feature was also estimated from the average pixel level within the best-fitting elliptical area encompassing the feature, relative to the average within surrounding annuli defined by an ellipse with 1.5 or 2 times the area.


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

Paras CL, Webster MA - Front Psychol (2013)

Examples of the faces reported by observers. After identifying and describing the face, observers drew on the image to indicate the perceived position and shape of features. Different features were coded with different colors (e.g., red for eyes, blue for nose, etc.) so that their dimensions could be analyzed afterward.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Examples of the faces reported by observers. After identifying and describing the face, observers drew on the image to indicate the perceived position and shape of features. Different features were coded with different colors (e.g., red for eyes, blue for nose, etc.) so that their dimensions could be analyzed afterward.
Mentions: After completing this labeling, the observers next identified the visible features of the face from a menu that included eyes, nose, mouth, ears, eyebrows, and head outline. For each they used a graphics pad to point to the center of the relevant feature, whose coordinates were then recorded, and also used a drop-down menu to record the distinctiveness of the feature. Finally, they next used the graphics pad to outline or fill in the contours of each feature by drawing on the image. These drawings were stored by overwriting the pixel values in a copy of the image, using different colors for each chosen feature so that these could be distinguished for subsequent analysis. Examples of faces drawn by the observers (who varied widely in artistic talent) are illustrated in Figure 2. Once these steps were completed the original image was redisplayed so that observers could look for additional faces. Typically many faces were detected in a single image. When observers felt they could no longer find new ones, they advanced to the next image, and repeated the sequence of responses. Images were shown in random order both within and across subjects. The drawings were analyzed by fitting ellipses to each selected feature to estimate the position, orientation, and aspect ratio of the smallest ellipse that encompassed 95% of the chosen pixels. The luminance contrast of the feature was also estimated from the average pixel level within the best-fitting elliptical area encompassing the feature, relative to the average within surrounding annuli defined by an ellipse with 1.5 or 2 times the area.

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