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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

Evoked potentials for face images or different variants of the noise images for three observers. Responses to realistic faces are shown by the black trace and elicit the only clear N170 response.
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Figure 13: Evoked potentials for face images or different variants of the noise images for three observers. Responses to realistic faces are shown by the black trace and elicit the only clear N170 response.

Mentions: Raw plots of the N170 amplitude versus latency for each observer are shown in Figure 13. Real faces elicited a strong N170 response. This was substantially larger than for any of the noise images, which in contrast showed little difference from each other. For example, normalized amplitudes of the N170 significantly differed for faces versus noise alone [t(2) = −15.6, p = 0.004] or versus the vertically symmetric noise with added eyes [t(2) = −21.6, p = 0.002]. In contrast, responses to these two noise patterns did not differ [t(2) = −2.25, p = 0.15], despite the fact that they varied substantially in their face-like appearance. The amplitude differences could potentially have occurred if the time to recognize the stimulus as a face were more variable for the noise (so that averaging across trials for the same stimulus onset washed out large peaks but with variable latency). However, this would predict longer average latencies for the noise images, which was not observed (e.g., mean latencies did not differ for the face and two noise types compared above [F(2,6) = 2.07, p = 0.21]. These results are limited to only a small sample of tested observers, and moreover cannot rule out the possibility that certain images within a given noise category might have evoked a stronger N170 (e.g., because they happened to resemble an actual face much more). However, like the preceding tasks, they are again consistent with the conclusion that the noise images fail to evoke some of the visual responses characteristic of actual faces.


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

Paras CL, Webster MA - Front Psychol (2013)

Evoked potentials for face images or different variants of the noise images for three observers. Responses to realistic faces are shown by the black trace and elicit the only clear N170 response.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 13: Evoked potentials for face images or different variants of the noise images for three observers. Responses to realistic faces are shown by the black trace and elicit the only clear N170 response.
Mentions: Raw plots of the N170 amplitude versus latency for each observer are shown in Figure 13. Real faces elicited a strong N170 response. This was substantially larger than for any of the noise images, which in contrast showed little difference from each other. For example, normalized amplitudes of the N170 significantly differed for faces versus noise alone [t(2) = −15.6, p = 0.004] or versus the vertically symmetric noise with added eyes [t(2) = −21.6, p = 0.002]. In contrast, responses to these two noise patterns did not differ [t(2) = −2.25, p = 0.15], despite the fact that they varied substantially in their face-like appearance. The amplitude differences could potentially have occurred if the time to recognize the stimulus as a face were more variable for the noise (so that averaging across trials for the same stimulus onset washed out large peaks but with variable latency). However, this would predict longer average latencies for the noise images, which was not observed (e.g., mean latencies did not differ for the face and two noise types compared above [F(2,6) = 2.07, p = 0.21]. These results are limited to only a small sample of tested observers, and moreover cannot rule out the possibility that certain images within a given noise category might have evoked a stronger N170 (e.g., because they happened to resemble an actual face much more). However, like the preceding tasks, they are again consistent with the conclusion that the noise images fail to evoke some of the visual responses characteristic of actual faces.

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