The effects of coarseness of quantisation, exposure duration, and selective spatial attention on the perception of spatially quantised ('blocked') visual images

Coarse-to-Fine(r) Automatic Familiar Face Recognition in the Human Brain

At what level of spatial resolution can the human brain recognize a familiar face in a crowd of strangers? Does it depend on whether one approaches or rather moves back from the crowd? To answer these questions, 16 observers viewed different unsegmented images of unfamiliar faces alternating at 6 Hz, with spatial frequency (SF) content progressively increasing (i.e., coarse-to-fine) or decreasing (fine-to-coarse) in different sequences. Variable natural images of celebrity faces every sixth stimulus generated an objective neural index of single-glanced automatic familiar face recognition (FFR) at 1 Hz in participants' electroencephalogram (EEG). For blurry images increasing in spatial resolution, the neural FFR response over occipitotemporal regions emerged abruptly with additional cues at about 6.3-8.7 cycles/head width, immediately reaching amplitude saturation. When the same images progressively decreased in resolution, the FFR response disappeared already below 12 cycles/head width, thus providing no support for a predictive coding hypothesis. Overall, these observations indicate that rapid automatic recognition of heterogenous natural views of familiar faces is achieved from coarser visual inputs than generally thought, and support a coarse-to-fine FFR dynamics in the human brain.

When Beauty Breaks Down: Investigation of the Effect of Spatial Quantisation on Aesthetic Evaluation of Facial Images

Research on the perception of facial attractiveness has been dominated by aspects of averageness, symmetry, and secondary sex characteristics of faces. Almost absent is systematic research on the spatial scale (coarseness) of detail sufficient to carry information about facial attractiveness. In the present study, subjects were asked to evaluate the attractiveness of faces while the coarseness of detail of the face images was systematically decreased. Subjects discriminated a set of attractive faces from the set of unattractive faces when the coarseness of spatial quantisation changed from 10 to 17 pixels per face. Some of the faces regarded as attractive had the steepest shift in the rating towards the more attractive end of the scale at different resolutions. Once perceived as attractive in the coarse scale of image resolution, the faces generally did not return to the unattractive group with a subsequent finer scale of description. No single critical scale of detail was revealed that would have dramatically changed the perception of facial attractiveness from uncertain to distinct.

Long-term expertise with artificial objects increases visual competition with early face categorization processes

The degree of commonality between the perceptual mechanisms involved in processing faces and objects of expertise is intensely debated. To clarify this issue, we recorded occipito-temporal event-related potentials in response to faces when concurrently processing visual objects of expertise. In car experts fixating pictures of cars, we observed a large decrease of an evoked potential elicited by face stimuli between 130 and 200 msec, the N170. This sensory suppression was much lower when the car and face stimuli were separated by a 200-msec blank interval. With and without this delay, there was a strong correlation between the face-evoked N170 amplitude decrease and the subject's level of car expertise as measured in an independent behavioral task. Together, these results show that neural representations of faces and nonface objects in a domain of expertise compete for visual processes in the occipito-temporal cortex as early as 130-200 msec following stimulus onset.

Face perception: An integrative review of the role of spatial frequencies

The aim of this article is to reinterpret the results obtained from the research analyzing the role played by spatial frequencies in face perception. Two main working lines have been explored in this body of research: the critical bandwidth of spatial frequencies that allows face recognition to take place (the masking approach), and the role played by different spatial frequencies while the visual percept is being developed (the microgenetic approach). However, results obtained to date are not satisfactory in that no single explanation accounts for all the data obtained from each of the approaches. We propose that the main factor for understanding the role of spatial frequencies in face perception depends on the interaction between the demands of the task and the information in the image (the diagnostic recognition approach). Using this new framework, we review the most significant research carried out since the early 1970s to provide a reinterpretation of the data obtained.

Variations in backward masking with different masking stimuli: II. The effects of spatially quantised masks in the light of local contour interaction, interchannel inhibition, perceptual retouch, and substitution theories

In part I we showed that with spatially non-overlapping targets and masks both local metacontrast-like interactions and attentional processes are involved in backward masking. In this second part we extend the strategy of varying the contents of masks to pattern masking where targets and masks overlap in space, in order to compare different masking theories. Images of human faces were backward-masked by three types of spatially quantised masks (the same faces as targets, faces different from targets, and Gaussian noise with power spectra typical for faces). Configural characteristics, rather than the spectral content of the mask, predicted the extent of masking at relatively long stimulus onset asynchronies (SOAs). This poses difficulties for the theory of transient-on-sustained inhibition as the principal mechanism of masking and also for local contour interaction being a decisive factor in pattern masking. The scale of quantisation had no effect on the masking capacity of noise masks and a strong effect on the capacity of different-face masks. Also, the decrease of configural masking with an increase in the coarseness of the quantisation of the mask highlights ambiguities inherent in the re-entrance-based substitution theory of masking. Different masking theories cannot solve the problems of masking separately. They should be combined in order to create a complex, yet comprehensible mode of interaction for the different mechanisms involved in visual backward masking.

Forward masking of faces by spatially quantized random and structured masks: On the roles of wholistic configuration, local features, and spatial-frequency spectra in perceptual identification

The forward masking of faces by spatially quantized masking images was studied. Masks were used in order to exert different types of degrading effects on the early representations in facial information processing. Three types of source images for masks were used: Same-face images (with regard to targets), different-face images, and random Gaussian noise that was spectrally similar to facial images. They were all spatially quantized over the same range of quantization values. Same-face masks had virtually no masking effect at any of the quantization values. Different-face masks had strong masking effects only with fine-scale quantization, but led to the same efficiency of recognition as in the same-face mask condition with the coarsest quantization. Moreover, compared with the noise-mask condition, coarsely quantized different-face masks led to a relatively facilitated level of recognition efficiency. The masking effect of the noise mask did not vary significantly with the coarseness of quantization. The results supported neither a local feature processing account, nor a generalized spatial-frequency processing account, but were consistent with the microgenetic configuration-processing theory of face recognition. Also, the suitability of a spatial quantization technique for image configuration processing research has been demonstrated.

Usage of spatial scales for the categorization of faces, objects, and scenes

The role of spatial scales (or spatial frequencies) in the processing of faces, objects, and scenes has recently seen a surge of research activity. In this review, we will critically examine two main theories of scale usage. The fixed theory proposes that spatial scales are used in a fixed, perceptually determined order (coarse to fine). The flexible theory suggests instead that usage of spatial scales is flexible, depending on the requirements of visual information for the categorization task at hand. The implications of the theories are examined for face, object, and scene categorization, attention, perception, and representation.

Hearing by eye: how much spatial degradation can be tolerated?

In the McGurk effect (McGurk and MacDonald, 1976 Nature 264 746-748), illusory auditory perception is produced if the visual information from lip movements is discrepant from the auditory information from the voice. A study is reported of the tolerance of the effect to varying levels of spatial degradation (videotaped images of a speaker's face were quantised by a mosaic transform). The illusory effect systematically decreased with an increase in the coarseness of the spatial quantisation. However, even with the coarsest level (11.2 pixels/face) the illusion did not completely disappear. In addition, those participants who did not experience the illusion nevertheless showed the effects of auditory-visual interaction in their clarity ratings of the auditory stimulus. It is concluded that auditory-visual interaction in visible speech perception is based on relatively coarse-spatial-scale information.

Dr. Angry and Mr. Smile: when categorization flexibly modifies the perception of faces in rapid visual presentations

Are categorization and visual processing independent, with categorization operating late, on an already perceived input, or are they intertwined, with the act of categorization flexibly changing (i.e. cognitively penetrating) the early perception of the stimulus? We examined this issue in three experiments by applying different categorization tasks (gender, expressive or not, which expression and identity) to identical face stimuli. Stimuli were hybrids: they combined a man or a woman with a particular expression at a coarse spatial scale with a face of the opposite gender with a different expression at the fine spatial scale. Results suggested that the categorization task changes the spatial scales preferentially used and perceived for rapid recognition. A perceptual set effect is shown whereby the scale preference of an important categorization (e.g. identity) transfers to resolve other face categorizations (e.g. expressive or not, which expression). Together, the results suggest that categorization can be closely bound to perception.

Integration of physical and semantic information in object processing

Physiological studies report independent processing pathways for form and colour information. A more-complex picture on human subjects has previously been reported. A sequential matching task was used that was based on a physical property of an object and in which semantic relations between stimuli were manipulated. Performance was affected by semantic information when matching was based on a property of the form of an object (its orientation, shape, or size). Effects of semantic information were eliminated when matching was based on the colour of a local part of an object but were found again when subjects matched pictures on the basis of the percentage of a colour integrated across the shape boundary. The results suggest independent selection mechanisms in vision in which selection by local colour can be based on inhibition of the form-processing pathway whilst processing of the global configuration of the form of an object activates automatically the identification process.