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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

Fixation patterns for two observers while scanning a realistic face or different versions of the noise images. Histograms to the right show the number of fixations within a region containing the eyes or within regions above or below the eyes.
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Figure 12: Fixation patterns for two observers while scanning a realistic face or different versions of the noise images. Histograms to the right show the number of fixations within a region containing the eyes or within regions above or below the eyes.

Mentions: In the remaining tasks, we turned to responses that did not require distinguishing individuals but again simply processing the image as a face. In the first case we monitored eye movements to examine whether subjects would scan the noise images in different ways depending on whether or not they perceived them as faces. Observers tend to view actual faces with characteristic fixation patterns that focus on prominent facial features including the eyes and mouth (Yarbus, 1967). In fact plots of the fixation locations tend to recreate an image of the inspected face (Figure 12). If the added blobs induced a strong face percept, then observers might similarly focus their scans on the illusory eye and mouth/nose regions of the image. Four observers were tested and told to inspect a series of images while their eye movements were recorded with a CRS video eye tracker. They were instructed to scan each image to determine if it was the same as the image which preceded it. This was done to ensure the observers maintained attention and scrutinized each image. Twenty images from each category were displayed for 5 s each, with the category randomized across trials. Fixation points were defined as fixations lasting at least 60 ms with a distance of ten pixels away from the three previous averaged samples, which were recorded every 20 ms.


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

Paras CL, Webster MA - Front Psychol (2013)

Fixation patterns for two observers while scanning a realistic face or different versions of the noise images. Histograms to the right show the number of fixations within a region containing the eyes or within regions above or below the eyes.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 12: Fixation patterns for two observers while scanning a realistic face or different versions of the noise images. Histograms to the right show the number of fixations within a region containing the eyes or within regions above or below the eyes.
Mentions: In the remaining tasks, we turned to responses that did not require distinguishing individuals but again simply processing the image as a face. In the first case we monitored eye movements to examine whether subjects would scan the noise images in different ways depending on whether or not they perceived them as faces. Observers tend to view actual faces with characteristic fixation patterns that focus on prominent facial features including the eyes and mouth (Yarbus, 1967). In fact plots of the fixation locations tend to recreate an image of the inspected face (Figure 12). If the added blobs induced a strong face percept, then observers might similarly focus their scans on the illusory eye and mouth/nose regions of the image. Four observers were tested and told to inspect a series of images while their eye movements were recorded with a CRS video eye tracker. They were instructed to scan each image to determine if it was the same as the image which preceded it. This was done to ensure the observers maintained attention and scrutinized each image. Twenty images from each category were displayed for 5 s each, with the category randomized across trials. Fixation points were defined as fixations lasting at least 60 ms with a distance of ten pixels away from the three previous averaged samples, which were recorded every 20 ms.

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