Spatial Frequency Bands Research Articles

Natural scenes have matched amplitude-modulated sounds that systematically influence visual scanning

We have previously demonstrated a linear perceptual relationship between auditory amplitude-modulation (AM) rate and visual spatial-frequency using gabors as the visual stimuli. Can this frequency-based auditory–visual association influence perception of natural scenes? Participants consistently matched specific auditory AM rates to diverse visual scenes (nature, urban, and indoor). A correlation analysis indicated that higher subjective density ratings were associated with faster AM-rate matches. Furthermore, both the density ratings and AM-rate matches were relatively scale invariant, suggesting that the underlying crossmodal association is between visual coding of object-based density and auditory coding of AM rate. Based on these results, we hypothesized that concurrently presented fast (7 Hz) or slow (2 Hz) AM-rates might influence how visual attention is allocated to dense or sparse regions within a scene. We tested this hypothesis by monitoring eye movements while participants examined scenes for a subsequent memory task. To determine whether fast or slow sounds guided eye movements to specific spatial frequencies, we computed the maximum contrast energy at each fixation across 12 spatial frequency bands ranging from 0.06–10.16 cycles/degree. We found that the fast sound significantly guided eye movements toward regions of high spatial frequency, whereas the slow sound guided eye movements away from regions of high spatial frequency. This suggests that faster sounds may promote a local scene scanning strategy, acting as a ‘filter’ to individuate objects within dense regions. Our results suggest that auditory AM rate and visual object density are crossmodally associated, and that this association can modulate visual inspection of scenes.

Perceptual Learning of Inverted Faces across Different Spatial Frequency Bands

Practicing a perceptual task can improve the ability to detect, discriminate, and identify stimuli, a phenomenon known as perceptual learning (1). Improvements have been found for simple and complex visual stimuli, including upright faces (2,3). However, little is known about the effects of practice on recognition of inverted faces (4,5). Here we hypothesized that adults might be better at learning to recognize inverted faces if trained with low spatial frequency images (<5 cpi; LSF) than full spectrum (FULL) or high spatial frequency images (>24 cpi; HSF) since newborns learn to recognize upright faces despite poor visual acuity (6). We trained 3 groups of 16 adults in a 10-AFC task with LSF, HSF or FULL inverted faces presented with different viewpoints. Participants were exposed either to the same or a different set of faces on Day 2. Although reaction times became significantly faster for all groups during training, accuracy improved only in the FULL (14%) and HSF (7%) groups. In contrast, the LSF group's overall improvement was only 1% (Fig1). Improvements from before to after training were assessed by comparisons to an untrained control group on 4 tasks. The FULL group showed more improvement in both accuracy and reactions time than controls on the delayed matching task of full spectrum inverted faces, thereby demonstrating generalization of training to novel faces. They were also faster on the same task with upright faces. The HSF group showed increased and decreased holistic processing of full spectrum inverted and upright faces, respectively, as indexed by reaction times on the composite face effect. Despite no improvement in accuracy during training, the LSF group improved more than controls on reaction times to match simultaneously presented full-spectrum inverted faces. These results suggest that perceptual learning of inverted faces and its generalization depend strongly on their spatial frequency content.

The horizontal tuning of face perception relies on the processing of intermediate and high spatial frequencies

It was recently shown that expert face perception relies on the extraction of horizontally oriented visual cues. Picture-plane inversion was found to eliminate horizontal, suggesting that this tuning contributes to the specificity of face processing. The present experiments sought to determine the spatial frequency (SF) scales supporting the horizontal tuning of face perception. Participants were instructed to match upright and inverted faces that were filtered both in the frequency and orientation domains. Faces in a pair contained horizontal or vertical ranges of information in low, middle, or high SF (LSF, MSF, or HSF). Our findings confirm that upright (but not inverted) face perception is tuned to horizontal orientation. Horizontal tuning was the most robust in the MSF range, next in the HSF range, and absent in the LSF range. Moreover, face inversion selectively disrupted the ability to process horizontal information in MSF and HSF ranges. This finding was replicated even when task difficulty was equated across orientation and SF at upright orientation. Our findings suggest that upright face perception is tuned to horizontally oriented face information carried by intermediate and high SF bands. They further indicate that inversion alters the sampling of face information both in the orientation and SF domains.

Low and high spatial frequencies are most useful for drawing.

What perceptual information do artists use to accurately render what they see? To answer this question, we investigated the utility of low, middle, and high spatial frequency bands for drawing. Untrained artists drew portraits from four spatial frequency bands (unfiltered, low, middle, and high). Raters judged the accuracy of those drawings compared to images of either the same or an unfiltered version of the face. Contrary to predictions based on the useful spatial frequencies for face recognition, which favor middle spatial frequencies (MSFs), the results showed that low spatial frequencies (LSFs) and high spatial frequencies (HSFs) were more useful for drawing, and the unfiltered condition produced the best drawings. Thus, the information most useful for drawing faces is not the same as that for recognizing faces. Specifically, artists may utilize the global configuration information carried in LSFs and the edge and detail information carried in HSFs to render accurate drawings.

Spatial frequency and visual discomfort

Images created from noise filtered to have an approximately 1/f amplitude spectrum were altered by adding excess energy concentrated at various spatial frequencies. The effects of this manipulation on judgements of visual discomfort were studied. Visual noise with a 1/f amplitude spectrum (typical of natural images) was judged more comfortable than any image with a relative increase in contrast energy within a narrow spatial frequency band. A peak centred on 0.375–1.5 cycles/degree of spatial frequency was consistently judged as more uncomfortable than a peak at a higher spatial frequency. This finding was robust to slight differences in eccentricity, and when stimuli were matched for perceived contrast across spatial frequency. These findings are consistent with the idea that deviation from the statistics of natural images could cause discomfort because the visual system is optimised to encode images with the particular statistics typical of natural scenes.

Transmission of colour and acuity signals by parvocellular cells in marmoset monkeys

The red-green axis of colour vision evolved recently in primate evolutionary history. Signals serving red-green colour vision travel together with signals serving spatial vision, in the parvocellular (PC) division of the subcortical visual pathway. However, the question of whether receptive fields of PC pathway cells are specialized to transmit red-green colour signals remains unresolved. We addressed this question in single-cell recordings from the lateral geniculate nucleus of anaesthetized marmosets. Marmosets show a high proportion of dichromatic (red-green colour-blind) individuals, allowing spatial and colour tuning properties of PC cells to be directly compared in dichromatic and trichromatic visual systems. We measured spatial frequency tuning for sine gratings that provided selective stimulation of individual photoreceptor types. We found that in trichromatic marmosets, the foveal visual field representation is dominated by red-green colour-selective PC cells. Colour selectivity of PC cells is reduced at greater eccentricities, but cone inputs to centre and surround are biased to create more selectivity than predicted by a purely 'random wiring' model. Thus, one-to-one connections in the fovea are sufficient, but not necessary, to create colour-selective responses. The distribution of spatial tuning properties for achromatic stimuli shows almost complete overlap between PC cells recorded in dichromatic and trichromatic marmosets. These data indicate that transmission of red-green colour signals has been enabled by centre-surround receptive fields of PC cells, and has not altered the capacity of PC cells to serve high-acuity vision at high stimulus contrast.

Shape space analysis of structures in bat biosonar.

Sound diffracting shapes such as the noseleaves and outer ears are prominent features of the biosonar systems in bats. Across different bat species, a remarkable diversity exists in the shapes of these structures. Interspecific differences between shapes are found in global shape properties such as size and aspect ratio as well as in local features such as flaps, ridges, and grooves. Because of the irregular shapes of these biological structures, the relationship between physical shape and acoustic function across all their different shapes is difficult to comprehend. As a first step to address this problem, an attempt is made to describe the different pinna geometries in a shape space intended to capture the salient trends in biological variability. Descriptions of variability require an alignment of shapes. This can be achieved by virtue of invariant features within a low spatial frequency band. Here, modal analysis is used for this purpose. The shapes can be transformed by mapping each point into a new space defined by the amplitudes of the shape’s vibration eigenmodes. The acoustic properties of the shapes can be changed significantly by local features. Hence, local shape descriptors are used to quantify these features and establish correspondences across different species.

Single-exposure two-dimensional superresolution in digital holography using a vertical cavity surface-emitting laser source array

We present a new implementation capable of producing two-dimensional (2D) superresolution (SR) imaging in a single exposure by aperture synthesis in digital lensless Fourier holography when using angular multiplexing provided by a vertical cavity surface-emitting laser source array. The system performs the recording in a single CCD snapshot of a multiplexed hologram coming from the incoherent addition of multiple subholograms, where each contains information about a different 2D spatial frequency band of the object's spectrum. Thus, a set of nonoverlapping bandpass images of the input object can be recovered by Fourier transformation (FT) of the multiplexed hologram. The SR is obtained by coherent addition of the information contained in each bandpass image while generating an enlarged synthetic aperture. Experimental results demonstrate improvement in resolution and image quality.

Interpreting the effects of image manipulation on picture perception in pigeons (Columba livia) and humans (Homo sapiens).

The effects of picture manipulations on humans' and pigeons' performance were examined in a go/no-go discrimination of two perceptually similar categories, cat and dog faces. Four types of manipulation were used to modify the images. Mosaicization and scrambling were used to produce degraded versions of the training stimuli, while morphing and cell exchange were used to manipulate the relative contribution of positive and negative training stimuli to test stimuli. Mosaicization mainly removes information at high spatial frequencies, whereas scrambling removes information at low spatial frequencies to a greater degree. Morphing leads to complex transformations of the stimuli that are not concentrated at any particular spatial frequency band. Cell exchange preserves high spatial frequency details, but sometimes moves them into the "wrong" stimulus. The four manipulations also introduce high-frequency noise to differing degrees. Responses to test stimuli indicated that high and low spatial frequency information were both sufficient but not necessary to maintain discrimination performance in both species, but there were also species differences in relative sensitivity to higher and lower spatial frequency information.

Visual Chimaeras Obtained with the Riesz Transform

Similar to an auditory chimaera (Smith et al, 2002 Nature 416 87-90), a visual chimaera can be defined as a synthetic image which has the fine spatial structure of one natural image and the envelope of another image in each spatial frequency band. Visual chimaeras constructed in this way could be useful to vision scientists interested in the study of interactions between first-order and second-order visual processing. Although it is almost trivial to generate 1-D chimaeras by means of the Hilbert transform and the analytic signal, problems arise in multidimensional signals like images given that the partial directional Hilbert transform and current 2-D demodulation algorithms are anisotropic or orientation-variant procedures. Here, we present a computational procedure to synthesise visual chimaeras by means of the Riesz transform--an isotropic generalisation of the Hilbert transform for multidimensional signals--and the associated monogenic signal--the vector-valued function counterpart of the analytic signal in which the Riesz transform replaces the Hilbert transform. Examples of visual chimaeras are shown for same/different category images.

Diagnostic spatial frequencies and human efficiency for discriminating actions

Humans extract visual information from the world through spatial frequency (SF) channels that are sensitive to different scales of light-dark fluctuations across visual space. Using two methods, we measured human SF tuning for discriminating videos of human actions (walking, running, skipping and jumping). The first, more traditional, approach measured signal-to-noise ratio (s/n) thresholds for videos filtered by one of six Gaussian band-pass filters ranging from 4 to 128 cycles/image. The second approach used SF “bubbles”, Willenbockel et al. (Journal of Experimental Psychology. Human Perception and Performance, 36(1), 122–135, 2010), which randomly filters the entire SF domain on each trial and uses reverse correlation to estimate SF tuning. Results from both methods were consistent and revealed a diagnostic SF band centered between 12-16 cycles/image (about 1-1.25 cycles/body width). Efficiency on this task was estimated by comparing s/n thresholds for humans to an ideal observer, and was estimated to be quite low (>.04%) for both experiments.

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.

Patients with schizophrenia are biased toward low spatial frequency to decode facial expression at a glance

Whereas patients with schizophrenia exhibit early visual processing impairments, their capacity at integrating visual information at various spatial scales, from low to high spatial frequencies, remains untested. This question is particularly acute given that, in ecological conditions of viewing, spatial frequency bands are naturally integrated to form a coherent percept.Here, 19 patients with schizophrenia and 16 healthy controls performed a rapid emotion recognition task with hybrid faces. Because these stimuli displayed in a single image two different facial expressions, in low (LSF) and high (HSF) spatial frequencies, the selected emotion probes which spatial scale is preferentially perceived. In a control experiment participants performed the same task with either low or high spatial frequency filtered faces.Results show that patients have a strong bias towards LSF with hybrid faces compared to healthy controls. However, both patients and healthy controls performed better with HSF filtered faces than with LSF filtered faces in the control experiment, demonstrating that the bias found with hybrid stimuli in patients was not due to an inability to process HSF.Whereas previous works found a LSF contrast deficit in schizophrenia, our results suggest a deficit in the normal time course of concurrently perceiving LSF and HSF. This early visual processing impairment is likely to contribute to the difficulties of patients with schizophrenia with facial processing and therefore social interaction.

Brief Report: Developing Spatial Frequency Biases for Face Recognition in Autism and Williams Syndrome

The current study investigated whether contrasting face recognition abilities in autism and Williams syndrome could be explained by different spatial frequency biases over developmental time. Typically-developing children and groups with Williams syndrome and autism were asked to recognise faces in which low, middle and high spatial frequency bands were masked. All three groups demonstrated a gradual specialisation toward the mid-band. However, while the use of high spatial frequencies decreased in control and autism groups over development, the Williams syndrome group did not display a bias toward this band at any point. These data demonstrate that typical outcomes can be achieved through atypical developmental processes, and confirm the importance of cross-syndrome studies in the investigation of developmental disorders.

Effects of spatial frequency bands on perceptual decision: It is not the stimuli but the comparison

Effects of spatial frequency bands on perceptual decision: It is not the stimuli but the comparison

Effects of spatial frequency bands on perceptual decision: It is not the stimuli but the comparison

Observers performed three between- and two within-category perceptual decisions with hybrid stimuli comprising low and high spatial frequency (SF) images. We manipulated (a) attention to, and (b) congruency of information in the two SF bands. Processing difficulty of the different SF bands varied across different categorization tasks: house-flower, face-house, and valence decisions were easier when based on high SF bands, while flower-face and gender categorizations were easier when based on low SF bands. Larger interference also arose from response relevant distracters that were presented in the "preferred" SF range of the task. Low SF effects were facilitated by short exposure durations. The results demonstrate that decisions are affected by an interaction of task and SF range and that the information from the non-attended SF range interfered at the decision level. A further analysis revealed that overall differences in the statistics of image features, in particular differences of orientation information between two categories, were associated with decision difficulty. We concluded that the advantage of using information from one SF range over another depends on the specific task requirements that built on the differences of the statistical properties between the compared categories.

Recognizing famous people

In daily life, face identification requires that the observer select a single representation from hundreds if not thousands in memory. This breadth of choice is nearly impossible to replicate in the laboratory using newly learned faces, especially in the context of a Bubbles experiment (Gosselin & Schyns, 2001). In this study, we obviated this concern by studying the performance of observers in a face-naming task using 210 faces of celebrities. On each trial, we presented a face randomly sampled with Bubbles. We performed least-square multiple linear regressions on the location of the samples and on accuracy to pinpoint the facial features that were used effectively in this task. Correct face identification relied primarily on the eye areas in spatial frequency bands ranging from 4.37 to 70 cycles per face (cpf) and on the mouth and the nose in a spatial frequency band ranging from 8.75 to 17.5 cpf. A comparison with other studies (Caldara et al., 2005; Schyns, Bonnar, & Gosselin, 2002) in which Bubbles was used with a set of 10 newly learned faces revealed that although the eye areas were useful across studies, the mouth area and higher spatial frequencies gained in importance when few newly learned faces were used.

Spectral tunneling of lattice nonlocal solitons

We address spectral tunneling of walking spatial solitons in photorefractive media with nonlocal diffusion of the nonlinear response and an imprinted shallow optical lattice. In contrast to materials with local nonlinearities, where solitons travelling across the lattice close to the Bragg angle suffer large radiative losses, in photorefractive media with diffusion nonlinearity resulting in self-bending solitons survive when their propagation angle approaches and even exceeds the Bragg angle. In the spatial frequency domain this effect can be considered as tunneling through the band of spatial frequencies centered around the Bragg frequency where the spatial group velocity dispersion is positive.

The N170 Marks the End of the process -- Dynamics of Occipito-temporal integration of facial features across spatial frequency bands to categorize facial expressions of emotion

The N170 Marks the End of the process -- Dynamics of Occipito-temporal integration of facial features across spatial frequency bands to categorize facial expressions of emotion

Contrast sensitivity in 1/f noise considered across spatial frequency band

Contrast sensitivity in 1/f noise considered across spatial frequency band