Visual search for object orientation can be modulated by canonical orientation

The authors studied the influence of canonical orientation on visual search for object orientation. Displays consisted of pictures of animals whose axis of elongation was either vertical or tilted in their canonical orientation. Target orientation could be either congruent or incongruent with the object's canonical orientation. In Experiment 1, vertical canonical targets were detected faster when they were tilted (incongruent) than when they were vertical (congruent). This search asymmetry was reversed for tilted canonical targets. The effect of canonical orientation was partially preserved when objects were high-pass filtered, but it was eliminated when they were low-pass filtered, rendering them as unfamiliar shapes (Experiment 2). The effect of canonical orientation was also eliminated by inverting the objects (Experiment 3) and in a patient with visual agnosia (Experiment 4). These results indicate that orientation search with familiar objects can be modulated by canonical orientation, and they indicate a top-down influence on orientation processing.     

The role of low-spatial frequencies in lexical decision and masked priming

Spatial frequency filtering was used to test the hypotheses that low-spatial frequency information in printed text can: (1) lead to a rapid lexical decision or (2) facilitate word recognition. Adult proficient readers made lexical decisions in unprimed and masked repetition priming experiments with unfiltered, low-pass, high-pass and notch filtered letter strings. In the unprimed experiments, a filtered target was presented for 105 or 400 ms followed by a pattern mask. Sensitivity (d′) was lowest for the low-pass filtered targets at both durations with a bias towards a ‘non-word’ response. Sensitivity was higher in the high-pass and notch filter conditions. In the priming experiments, a forward mask was followed by a filtered prime then an unfiltered target. Primed words, but not non-words, were identified faster than unprimed words in both the low-pass and high-pass filtered conditions. These results do not support a unique role for low-spatial frequency information in either facilitating or making rapid lexical decisions.     

Sex differences in mental rotation strategy

When humans decide whether two visual stimuli are identical or mirror images of each other and one of the stimuli is rotated with respect to the other, the time discrimination takes usually increases as a rectilinear function of the orientation disparity. On the average, males perform this mental rotation at a faster angular speed than females. This experiment required the rotation of both mirror-image-different and non-mirror-different stimuli. The polygonal stimuli were presented in either spatially unfiltered, high-pass or low-pass filtered versions. All stimulus conditions produced mental rotation-type effects but with graded curvilinear trends. Women rotated faster than men under all conditions, an infrequent outcome in mental rotation studies. Overall, women yielded more convexly curvilinear response functions than men. For both sexes the curvilinearity was more pronounced under the non-mirror-different, low-pass stimulus condition than under the mirror different, high-pass stimulus condition. The results are considered as supporting the occurrence of two different mental rotation strategies and as suggesting that the women were predisposed to use efficiently an analytic feature rotation strategy, while the men were predisposed to employ efficiently a holistic pattern rotation strategy. It is argued that the overall design of this experiment promoted the application of an analytic strategy and thus conferred an advantage to the female participants.     

The effects of spatial frequency overlap on face recognition

The effects of spatial frequency overlap between pairs of low-pass versus high-pass images on face recognition and matching were examined in 6 experiments. Overlap was defined as the range of spatial frequencies shared by a pair of filtered images. This factor was manipulated by processing image pairs with high-pass/low-pass filter pairs whose 50% cutoff points varied in their separation from one another. The effects of the center frequency of filter pairs were also investigated. In general, performance improved with greater overlap and higher center frequency. In control conditions, the image pairs were processed with identical filters and thus had complete overlap. Even severely filtered low-pass or high-pass images in these conditions produced superior performance. These results suggest that face recognition is more strongly affected by spatial frequency overlap than by the frequency content of the images.     

Temporal integration of spatially filtered visual images.

Factors which govern the temporal integration of spatial information were examined in a group of five experiments. A series of high-pass and low-pass spatially filtered versions of a visual scene were generated. Observers' ratings of these filtered versions of the scene for perceived image quality indicated that quality was determined both by the bandwidth of spatial information and the presence of high-spatial-frequency edge information. When sequences of three different versions of the scene were presented over an interval of 120 ms the perceived quality of the resulting composite image was determined both from the ratings of the individual components of that sequence and from the order in which these components were presented. When the order of spatial information in a sequence moved from coarse to fine detail the perceived quality of the composite image was significantly better than when the order moved from fine to coarse. This evidence of a coarse-to-fine bias in pattern integration was further investigated with a detection paradigm. The pattern of errors once again indicated that temporal integration of spatial information was superior when a coarse-to-fine mode of information delivery was employed. Taken together the data indicate that the pattern-integration mechanism has an inherent order bias and does not accumulate spatial information so efficiently when the 'natural' coarse-to-fine order is violated.     

Effects of spatial frequency content on classification of face gender and expression

The role of different spatial frequency bands on face gender and expression categorization was studied in three experiments. Accuracy and reaction time were measured for unfiltered, low-pass (cut-off frequency of 1 cycle/deg) and high-pass (cutoff frequency of 3 cycles/deg) filtered faces. Filtered and unfiltered faces were equated in root-mean-squared contrast. For low-pass filtered faces reaction times were higher than unfiltered and high-pass filtered faces in both categorization tasks. In the expression task, these results were obtained with expressive faces presented in isolation (Experiment 1) and also with neutral-expressive dynamic sequences where each expressive face was preceded by a briefly presented neutral version of the same face (Experiment 2). For high-pass filtered faces different effects were observed on gender and expression categorization. While both speed and accuracy of gender categorization were reduced comparing to unfiltered faces, the efficiency of expression classification remained similar. Finally, we found no differences between expressive and non expressive faces in the effects of spatial frequency filtering on gender categorization (Experiment 3). These results show a common role of information from the high spatial frequency band in the categorization of face gender and expression.     

The role of high spatial frequencies in face perception

The relevance of low and high spatial-frequency information for the recognition of photographs of faces has been investigated by testing recognition of faces that have been either low-pass (LP) or high-pass (HP) filtered in the spatial-frequency domain. The highest resolvable spatial frequency was set at 15 cycles per face width (cycles fw-1). Recognition was much less accurate for images that contained only the low spatial frequencies (up to 5 cycles fw-1) than for images that contained only spatial frequencies higher than 5 cycles fw-1. For faces HP filtered above 8 cycles fw-1, recognition was almost as accurate as for faces LP filtered below 8 cycles fw-1, although the energy content of the latter greatly exceeded that of the former. These findings show that information conveyed by the higher spatial frequencies is not redundant. Rather, it is sufficient by itself to ensure recognition.     

Spatial frequency filtering and the direct control of fixation durations during scene viewing

The present study employed a saccade-contingent change paradigm to investigate the effect of spatial frequency filtering on fixation durations during scene viewing. Subjects viewed grayscale scenes while encoding them for a later memory test. During randomly chosen saccades, the scene was replaced with an alternate version that remained throughout the critical fixation that followed. In Experiment 1, during the critical fixation, the scene could be changed to high-pass and low-pass spatial frequency filtered versions. Under both conditions, fixation durations increased, and the low-pass condition produced a greater effect than the high-pass condition. In subsequent experiments, we manipulated the familiarity of scene information during the critical fixation by flipping the filtered scenes upside down or horizontally. Under these conditions, we observed lengthening of fixation durations but no difference between the high-pass and low-pass conditions, suggesting that the filtering effect is related to the mismatch between information extracted within the critical fixation and the ongoing scene representation in memory. We also conducted control experiments that tested the effect of changes to scene orientation (Experiment 2a) and the addition of color to a grayscale scene (Experiment 2b). Fixation distribution analysis suggested two effects on the distribution fixation durations: a fast-acting effect that was sensitive to all transsaccadic changes tested and a later effect in the tail of the distribution that was likely tied to the processing of scene information. These findings are discussed in the context of theories of oculomotor control during scene viewing.     

The effect of spatial frequency content on parameters of eye movements

Two experiments were conducted to examine the influence of the spatial frequency content of natural images on saccadic size and fixation duration. In the first experiment 10 pictures of natural textures were low-pass filtered (0.04-0.76 cycles/deg) and high-pass filtered (1.91-19.56 cycles/deg) and presented with the unfiltered originals in random order, each for 10 s, to 18 participants, with the instruction to inspect them in order to find a suitable name. The participants' eye movements were recorded. It was found that low-pass filtered images resulted in larger saccadic amplitudes compared with high-pass filtered images. A second experiment was conducted with natural stimuli selected for different power spectra which supported the results outlined above. In general, low-spatial frequencies elicit larger saccades associated with shorter fixation durations whereas high-spatial frequencies elicit smaller saccades with longer fixation durations.     

Categorizing facial identities, emotions, and genders: attention to high- and low-spatial frequencies by children and adults

Three age groups of participants (5-6 years, 7-8 years, adults) matched faces on the basis of facial identity. The procedure involved either low- or high-pass filtered faces or hybrid faces composed from two faces associated with different spatial bandwidths. The comparison stimuli were unfiltered faces. In the three age groups, the data indicated a significant bias for processing of low-pass information in priority. In a second task, participants were asked to identify the emotion (smiling or grimacing) or gender (male or female) of hybrid high-pass/low-pass faces. Opposite results emerged in the two tasks irrespective of the age group; the gender discrimination task indicated a bias for low-pass information, and the emotion task indicated a bias for high-pass information. These differences suggest independent processing routes for functionally different types of information such as emotion, gender, and identity. These routes are already established by 5 years of age.     

Motion aftereffects with horizontally moving sound sources in the free field

A horizontally moving sound was presented to an observer seated in the center of an anechoic chamber. The sound, either a 500-Hz low-pass noise or a 6300-Hz high-pass noise, repeatedly traversed a semicircular arc in the observer's front hemifield at ear level (distance: 1.5 m). At 10-sec intervals this adaptor was interrupted, and a 750-msec moving probe (a 500-Hz low-pass noise) was presented from a horizontal arc 1.6 m in front of the observer. During a run, the adaptor was presented at a constant velocity (-200 degrees to +200 degrees/sec), while probes with velocities varying from -10 degrees to +10 degrees/sec were presented in a random order. Observers judged the direction of motion (left or right) of each probe. As in the case of stimuli presented over headphones (Grantham & Wightman, 1979), an auditory motion aftereffect (MAE) occurred: subjects responded "left" to probes more often when the adaptor moved right than when it moved left. When the adaptor and probe were spectrally the same, the MAE was greater than when they were from different spectral regions; the magnitude of this difference depended on adaptor speed and was subject-dependent. It is proposed that there are two components underlying the auditory MAE: (1) a generalized bias to respond that probes move in the direction opposite to that of the adaptor, independent of their spectra; and (2) a loss of sensitivity to the velocity of moving sounds after prolonged exposure to moving sounds having the same spectral content.     

Faces are "spatial"--holistic face perception is supported by low spatial frequencies

Faces are perceived holistically, a phenomenon best illustrated when the processing of a face feature is affected by the other features. Here, the authors tested the hypothesis that the holistic perception of a face mainly relies on its low spatial frequencies. Holistic face perception was tested in two classical paradigms: the whole-part advantage (Experiment 1) and the composite face effect (Experiments 2-4). Holistic effects were equally large or larger for low-pass filtered faces as compared to full-spectrum faces and significantly larger than for high-pass filtered faces. The disproportionate composite effect found for low-pass filtered faces was not observed when holistic perception was disrupted by inversion (Experiment 3). Experiment 4 showed that the composite face effect was enhanced only for low spatial frequencies, but not for intermediate spatial frequencies known be critical for face recognition. These findings indicate that holistic face perception is largely supported by low spatial frequencies. They also suggest that holistic processing precedes the analysis of local features during face perception.     

The effects of figure/ground, perceived area, and target saliency on the luminosity threshold

Observers adjusted the luminance of a target region until it began to appear self-luminous, or glowing. In Experiment 1, the target was either a face-shaped region (figure) or a non-face-shaped region (ground) of identical area that appeared to be the face's background. In Experiment 2, the target was a square or a trapezoid of identical area that appeared as a tilted rectangle. In Experiment 3, the target was a square surrounded by square, circular, or diamond-shaped elements. Targets that (1) were perceived as figures, (2) were phenomenally small in area, or (3) did not group well with other elements in the array because of shape appeared self-luminous at significantly lower luminance levels. These results indicate that like lightness perception, the luminosity threshold is influenced by perceptual organization and is not based on low-level retinal processes alone.     

Acquisition of a same-different discrimination task by pigeons (Columba livia)

Four homing pigeons were trained to discriminate two figures simultaneously presented on an LCD screen. The figure was either a rectangle (A) or a square (B), and four combinations of the two figures, AA, AB, BA, BB, appeared in a pseudo-randomized order. The pigeons' task was to peck one of these figures based upon whether the two figures were identical or not. One pigeon successfully learned this discrimination, with proportions of correct responses above 90% in two consecutive sessions. Of the other birds, two performed above chance level but had difficulty meeting a learning criterion of above 80% in two consecutive sessions. All birds achieved this criterion when the combinations of figures presented were reduced to two. Results suggested that learning the present same-different discrimination is within the capacity of pigeons to a certain extent, although there exists considerable individual variation in the pigeons' skills to acquire complex discrimination.     

The effect of spatial-frequency filtering on the visual processing of global structure

In three experiments we measured reaction times (RTs) and error rates in identifying the global structure of spatially filtered stimuli whose spatial-frequency content was selected by means of three types of 2-D isotropic filters (Butterworth of order 2, Butterworth of order 10, and a filters with total or partial Gaussian spectral profile). In each experiment, low-pass (LP), bandpass (BP), and high-pass (HP) filtered stimuli, with nine centre or cut-off spatial frequencies, were used. Irrespective of the type of filter, the experimental results showed that: (a) RTs to stimuli with low spatial frequencies were shorter than those to stimuli with medium or high spatial frequencies, (b) RTs to LP filtered stimuli were nearly constant, but they increased in a nonmonotonic way with the filter centre spatial frequency in BP filtered stimuli and with the filter cut-off frequency in HP filtered stimuli, and (c) the identification of the global pattern occurred with all visible stimuli used, including BP and HP images without low spatial frequencies. To remove the possible influence of the energy, a fourth experiment was conducted with Gaussian filtered stimuli of equal contrast power (c(rms) = 0.065). Similar results to those described above were found for stimuli with spatial-frequency content higher than 2 cycles deg(-1). A model of isotropic first-order visual channels collecting the stimulus spectral energy in all orientations explains the RT data. A subsequent second-order nonlinear amplitude demodulation process, applied to the output of the most energetic first-order channel, could explain the perception of global structure of each spatially filtered stimulus, including images lacking low spatial frequencies.     

Goal attribution to schematic animals: do 6‐month‐olds perceive biological motion as animate?

Infants are sensitive to biological motion, but do they recognize it as animate? As a first step towards answering this question, two experiments investigated whether 6‐month‐olds selectively attribute goals to shapes moving like animals. We habituated infants to a square moving towards one of two targets. When target locations were switched, infants reacted more to movement towards a new goal than a new location – but only if the square moved non‐rigidly and rhythmically, in a schematic version of bio‐mechanical movement older observers describe as animal‐like ( Michotte, 1963 ). Goal attribution was specific to schematic animal motion: It did not occur if the square moved rigidly with the same rhythm as the animate stimulus, or if the square had the same amount of non‐rigid deformation, but in an inanimate configuration. The data would seem to show that perception of schematic animal motion is linked to a system for psychological reasoning from infancy. This in turn suggests that 6‐month‐olds may already interpret biological motion as animate.     

Area perception in simple geometrical figures

The results of experiments on visual perception of area of circles and squares are reported. Pairs of geometrical figures were presented simultaneously on an oscilloscope screen. While one of them was fixed, the other one was controlled by an experimental subject. The task of the subject was to match the area of the variable figure to the area of the fixed one. The obtained data show underestimation of the area of circle when compared with square. A mathematical model designed to explain this phenomenon is proposed here. The image function defined as a low-pass filtered (blurred) version of the figure is employed for this purpose. Then, instead of the position of the image function maxima, the position of a threshold value is used for area computation.     

The effect of spectral difference on auditory saltation

Auditory saltation is a spatiotemporal illusion in which the judged positions of sound stimuli are shifted toward subsequent stimuli that follow closely in time and space. In this study, the "reduced-rabbit" paradigm and a direct-location method were employed to investigate the effect of spectral sound content on the saltation illusion. Eighteen listeners were presented with sound sequences consisting of three high-pass or low-pass filtered noise bursts. Noise bursts within a sequence were either the same or differed in frequency. Listeners judged the position of the second sound using a hand pointer. When the time interval between the second and third sound was short, the target was shifted toward the location of the subsequent stimulus. This displacement effect did not depend on the spectral content of the first sound, but decreased substantially when the second and third sounds were different. The results indicated an effect of spectral difference on saltation that is discussed with regard to a recently proposed stimulus integration approach in which saltation was attributed to an interaction between perceptual processing of temporally proximate stimuli.     

Perceptual causality in the amodal completion of kinetic structures

Perceptual causality as an amodal completion of kinetic structures was demonstrated. The experimental situation was as follows: a square appeared on the left, moved from left to right till it touched one side of a stationary rectangle (a perceptual screen), and disappeared; after a while, another square appeared at the other side of the rectangle and moved right. The first square moved faster than the second one. Sometimes, two moving objects were perceived, with an amodal launching effect: the first moving object seemed to collide with the second one behind the screen. When both the screen and the occluding interval were small, despite the discrepancy of velocities, a single moving object was perceived, but the object seemed to abruptly change its speed behind the screen. The perception of an amodal completion of movement raises some theoretical issues: the discrepancy between amodal completion of kinetic structures and that of static ones, the problem of perceptual identity, and figure-ground segregation in dynamic scene. The dilemma of the naive subject will also be discussed. Received: 11 June 1997 / Accepted: 14 October 1998     

A study of orientation errors in response to Kohs-type figures(1)

In order to elucidate the nature of the orientation errors encountered when subjects are required to reproduce Kohs-type figures, subjects drawn from a culture where such errors are reported to be relatively common were required to reproduce orientation of simple figures. It was found that the responses made in the case of square figures showed a definite drift towards a “stable” orientation; the drift observed in the case of circular stimuli was too weak to permit an unambiguous interpretation. The relevance of these data to previous data on cross-cultural differences in responses to Kohs-type stimuli is briefly examined.