Limits...
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

Perceived locations (center pixel) of features in the images, illustrated for three observers. Top: eye positions; middle: nose positions; bottom: mouth positions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3569666&req=5

Figure 4: Perceived locations (center pixel) of features in the images, illustrated for three observers. Top: eye positions; middle: nose positions; bottom: mouth positions.

Mentions: The faces identified in the images varied widely in spatial layout, configuration, and size showing that a large range of spatial configurations could appear as a face. Moreover, while we did not record perceived viewpoint, informal observations, and reports suggest that almost all faces were perceived as frontal views and thus not foreshortened, again suggesting that a wide range of configurations can elicit a face percept. For the symmetric noise images we tested, the faces reported were almost without exception frontal view images aligned to the axis of symmetry. This can be seen in Figure 4, which plots the location reported for the eyes, which were symmetrically positioned about the midline, in comparison to the nose and mouth, which were tightly confined to the midline. The paucity of percepts of face profiles is notable. One possibility is that profiles require stronger cues for the head outline than frontal faces, for which the internal face features may be sufficient. Within the noise we used there are not strong percepts of separate figure and ground regions which may therefore have worked against perceiving head outlines.


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

Paras CL, Webster MA - Front Psychol (2013)

Perceived locations (center pixel) of features in the images, illustrated for three observers. Top: eye positions; middle: nose positions; bottom: mouth positions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Perceived locations (center pixel) of features in the images, illustrated for three observers. Top: eye positions; middle: nose positions; bottom: mouth positions.
Mentions: The faces identified in the images varied widely in spatial layout, configuration, and size showing that a large range of spatial configurations could appear as a face. Moreover, while we did not record perceived viewpoint, informal observations, and reports suggest that almost all faces were perceived as frontal views and thus not foreshortened, again suggesting that a wide range of configurations can elicit a face percept. For the symmetric noise images we tested, the faces reported were almost without exception frontal view images aligned to the axis of symmetry. This can be seen in Figure 4, which plots the location reported for the eyes, which were symmetrically positioned about the midline, in comparison to the nose and mouth, which were tightly confined to the midline. The paucity of percepts of face profiles is notable. One possibility is that profiles require stronger cues for the head outline than frontal faces, for which the internal face features may be sufficient. Within the noise we used there are not strong percepts of separate figure and ground regions which may therefore have worked against perceiving head outlines.

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