bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal Competition between Odorants: Effect of Different Time Intervals on the Perception of Monorhinic and Dichorhinic Binary Mixtures
Authors: Rouby Catherine , Holley André
Published: January 2007

Backward masking and its possible connection with the perception of odour mixtures has been investigated. Temporal competition between odorants in a binary mixture was tested by artificially creating a delay between one odour (the target) and a second, stronger, odour (the mask) during a single natural sniff. To test the influence of central versus peripheral competition, the same mixture was presented either monorhinically or dichorhinically. The delay (100 to 400 ms) did not influence intensity perception, indicating that intensities are integrated during the sniff irrespective of the temporal arrangement. In contrast, the number of qualities perceived was influenced by the delay: delays of 200 to 400 ms gave significant increases in the frequency of detection of a mixture, whereas synchronous mixtures favoured the perception of a single odour. Masking was also significantly stronger in dichorhinic mixtures.

These effects are discussed in terms of retroactive masking which seems to be enhanced by dichorhinic mixtures, suggesting that masking has an important central component.
Spatial Filtering and the Zöllner—Judd Geometrical Illusion: Further Studies
Authors: Earle David C , Maskell Stephen J
Published: January 2007

In a geometrical figure in which long vertical lines are each crossed by a series of short oblique lines, an illusory effect is obtained such that the orientations of the long lines are perceived as nonvertical and shifted away from the orientation of the oblique lines (the Zöllner illusion). In addition, the vertical separation between the crossing (oblique) lines is perceived as less than that if the crossing lines are horizontal (the Judd illusion). It has previously been shown that these two effects are closely related, and a single-process account has been proposed in which both effects are explained by a computational model involving band-pass spatial filtering of the figure by means of difference-of-Gaussians (DOG) filters. Two arguments are presented against the latter account. First, in an opposite-contrast-polarity figure with, for example, white vertical lines and black crossing lines on a mid-grey background, the peaks in the DOG filter output are such as to predict the reversal of the Zöllner—Judd effects. It is shown by demonstration that this prediction is disconfirmed, and that the normal effects are obtained. Second, it is shown that the normal Zöllner—Judd effects are obtained in the absence of the long vertical lines, and in the presence of anomalous contours. The latter effects are also in contradiction to the band-pass-filtering model. These findings are discussed in relation to a dual-process account of the Zöllner—Judd effects.
Evidence for Good Recovery of Lengths of Real Objects Seen with Natural Stereo Viewing
Authors: Frisby John P , Buckley David , Duke Philip A
Published: January 2007

Six experiments are described in which good performance of the task of matching the lengths of two stationary real objects, gnarled wooden sticks, under a variety of binocular viewing conditions, including variations in viewing distances was demonstrated. Relatively poor matching performance was observed when the sticks were viewed monocularly in oscillatory motion, or monocularly and stationary. The results suggest that stereo can support good representations of metric scene structure when length judgments of natural objects are required under (quasi-)natural viewing. The implications of these results for theories of structure from stereo and structure from motion are discussed.
Pooling of Vertical Disparities by the Human Visual System
Authors: Adams Wendy , Frisby John P , Buckley David , Gårding Jonas , Hippisley-Cox Stephen D , Porrill John
Published: January 2007

Two experiments are described in which the effects of scaling vertical disparities on the perceived amplitudes of dome-shaped surfaces depicted with horizontal disparities were examined. The Mayhew and Longuet-Higgins's theory and the regional-disparity-correction theory of Gar̊ding et al predict that scaling should generate a change in perceived depth appropriate to the viewing distance simulated by the scaled vertical disparities. Significant depth changes were observed, by means of a nulling task in which the vertical-disparity-scaling effect was cancelled by the observer choosing a pattern of horizontal disparities that made the dome-shaped surface appear flat. The sizes of the scaling effects were less than those predicted by either theory, suggesting that other cues to fixation distance such as oculomotor information played an appreciable role. In conditions in which 50% of the texture elements were given one value of vertical-disparity scaling and the remaining 50% were left unscaled, the size of the scaling effect on perceived depth could be accounted for by equally weighted pooling of the vertical-disparity information unless the two scalings were very dissimilar, in which case the lower scaling factor tended to dominate. These findings are discussed in terms of a Hough parameter estimation model of the vertical-disparity-pooling process.
The Depiction of Distance: A Bartelian Analysis
Authors: Deręgowski Jan B , Parker Denis M
Published: January 2007

Work by Bartel has shown that observers make systematic errors when attempting to set a receding row of staves at equal intervals, and make even-more-pronounced errors in the same direction when drawing a similar row; consequently, the factors that contribute to this systematic distortion in spatial representation were examined. The results indicate that the tendency to overestimate nearer distances and underestimate further distances in pictorial space may be enhanced both by increasing the size ratio of the nearest and furthest pictorial elements and by increasing the angle of convergence of represented parallel contours. However, it is clear that size ratio is the more powerful independent variable. The reasons for this discrepancy are discussed and an explanation of the pattern of pictorial distortion, in terms of a compromise between an objective representation of the relative estimated distance of the depicted distances and an inaccurately anticipated optical projection, is proffered.
Measurements of Colour Constancy by Using a Forced-Choice Matching Technique
Authors: Bramwell David I , Hurlbert Anya C
Published: January 2007

Colour constancy is typically measured with techniques involving asymmetric matching by adjustment, in which the observer views two scenes under different illuminants and adjusts the colour of a reference patch in one to match a test patch in the other. This technique involves an unnatural task, requiring the observer to predict and adjust colour appearance under an illumination shift. Natural colour constancy is more a simple matter of determining whether a colour is the same as or different from that seen under different illumination conditions. There are also technical disadvantages to the method of matching by adjustment, particularly when used to measure colour constancy in complex scenes. Therefore, we have developed and tested a two-dimensional method of constant-stimuli, forced-choice matching paradigm for measuring colour constancy. Observers view test and reference scenes haploscopically and simultaneously, each eye maintaining separate adaptation throughout a session. On each trial, a pair of test and reference patches against multicoloured backgrounds are presented, the reference patch colours being selected from a two-dimensional grid of displayable colours around the point of perfect colour constancy. The observer's task is to respond “same” or “different”. Fitting a two-dimensional Gaussian to the percentage of “different” responses yields (1) the subjective colour-constancy point, (2) the discrimination ellipse centred on this point, and (3) a map of changes in sensitivity to chromatic differences induced by the illuminant shift. The subjective colour-constancy point measured in this way shows smaller deviations from perfect colour constancy—under conditions of monocular adaptation—than previously reported; discrimination ellipses are several times larger than standard MacAdam ellipses; and chromatic sensitivity is independent of the direction of the illuminant shift, for broad distributions of background colours.
A Note on the Concept of the Visual Field in Neurology, Psychology, and Visual Neuroscience
Authors: Smythies John
Published: January 2007

Some current confusions in visual neuroscience and psychology over the use of the terms ‘visual field’, ‘field of vision’, ‘stimulus field’, and topographic ‘brain maps’ are reviewed. These are often used as synonyms, whereas they refer to quite different things. A plea is made that visual scientists should use these terms correctly to avoid conceptual and engineering confusion.
The Discriminability of Local Surface Structure
Authors: Norman J Farley , Todd James T
Published: January 2007

The ability of observers to discriminate depth and orientation differences between separated local regions on object surfaces was examined. The objects were defined by many optical sources of information simultaneously, including shading, texture, motion, and binocular disparity. Despite the full-cue nature of the displays, the observers' performance was relatively poor, with Weber fractions ranging from 10% to 40%. The Weber fractions were considerably lower for discriminations of surface-orientation differences than for similar discriminations of depth differences. The ability of observers to discriminate surface-orientation differences was approximately invariant over the separation of the regions in the projected image. In contrast, the ability to discriminate depth differences was highly influenced by the amount of image separation. This qualitative difference between the perception of depth intervals and surface-orientation differences suggests that knowledge of depths and orientations may be represented separately within the human visual system.
Mach-Band Attenuation by Adjacent Stimuli: Experiment and Filling-in Simulations
Authors: Pessoa Luiz
Published: January 2007

Mach bands are illusory bright and dark bands seen where a luminance plateau meets a ramp, as in half shadows or penumbras. It has previously been shown that Mach bands are attenuated by placing stimuli, such as bars, nearby. It was shown in an experiment in which Mach-band attenuation for bar and Craik–O'Brien stimuli was compared that they are equally effective in attenuating Mach bands. The results suggest that the abrupt luminance transition of a stimulus adjacent to a ramp is responsible for the attenuation. The findings are interpreted in terms of a recent filling-in model of brightness perception and the results of computer simulations of stimuli are shown.
Illusory Line Motion in Visual Search: Attentional Facilitation or Apparent Motion?
Authors: Kawahara Jun'ichiro , Yokosawa Kazuhiko , Nishida Shin'ya , Sato Takao
Published: January 2007

A line, presented instantaneously, is perceived to be drawn from one end when a dot is flashed at that end prior to the presentation of the line. Although this phenomenon, called illusory line motion, has been attributed to accelerated processing at the locus of attention, preattentive (stimulus-driven) motion mechanisms might also contribute to the line-motion sensation. We tested this possibility in an odd-target-search task. The stimulus display consisted of two, four, or eight pairs of dots and lines. All lines were presented on the same side of the dots (eg right), except for the target line, which was presented on the opposite side (left). Subjects were asked to report the presence or absence of the target, which was presented in half of the trials. Low error rates for target detection (about 10%) even when the display consisted of eight dot-line pairs (ie display size was eight) indicated that illusory line motion could be perceived simultaneously at many locations. The interstimulus interval (ISI) between the dots and lines (0–2176 ms) and the contrast polarity (both dots and lines were brighter than the background, or dots were darker and lines were brighter) were also manipulated. When an ISI of a few hundred milliseconds was inserted, target detection was nearly impossible with larger display sizes. When the contrast polarity was changed, the target-detection performance was impaired significantly, even with no ISI. Moreover, it was found that the effects of display size, ISI, and contrast polarity were comparable in searches for a two-dot apparent-motion target. These results support the idea that preattentive, apparent-motion mechanisms, as well as attentional mechanisms, contribute to illusory line motion.
Cognitive Salience of Haptic Object Properties: Role of Modality-Encoding Bias
Authors: Lederman Susan J , Summers Craig , Klatzky Roberta L
Published: January 2007

The influence of modality-encoding bias on the relative importance (‘cognitive salience’) of object shape, size, and material, with the last determined by weight and thermal variations, was examined. Experiment 1 confirmed that for these stimulus objects all five properties were very accessible haptically, as measured by the time to identify the property level of each designated property; however, observers were still generally faster for geometric than material properties. In experiment 2, the influence of modality-encoding bias on cognitive salience was assessed by using a task involving free sorting by similarity. As predicted, modality-encoding bias strongly influenced cognitive salience. Observers favoured sorting by material under haptic-bias instructions, and three-dimensional geometric properties (especially shape) under visual-bias instructions. Videotaped hand movements indicated that modality-encoding biases reflect long-term knowledge of the relative speed and precision of manual exploration patterns, rather than exploration of the current set of objects.
Perceptual Learning of Stereoacuity
Authors: Sowden Paul , Davies Ian , Rose David , Kaye Martin
Published: January 2007

It has often been noted that with repeated exposure to random-dot stereograms the time required to perceived depth decreases. Further, with extensive practice, stereoacuity thresholds have been shown to decrease. For both types of learning some researchers have reported specificity of the improvements to retinal location, and have thus suggested that the learning may be localised at early levels of visual processing, such as in primary visual cortex. However, these studies have not adequately ruled out the possibility that the specificity shown may be due to the operation of selective-spatial-attention mechanisms. In the present study this possibility was examined by training observers to judge the relative depth of a pair of stereograms presented equally often in two spatial locations, but stimuli were only presented with one direction of disparity (ie crossed or uncrossed) in any one location. Results indicated that, as expected, observers' judgments improved with practice. However, this improvement transferred completely to stimuli presented with the other direction of disparity in each location. Thus, it is argued that previous findings of retinal-location-specific improvements in stereoacuity may well be due to selective-spatial-attention mechanisms, rather than to learning localised at an early level of visual processing.
Descriptions of Visual Phenomena from Aristotle to Wheatstone
Authors: Wade Nicholas J
Published: January 2007

A history of the observational era of vision is presented through selected descriptions of phenomena by natural philosophers from Aristotle to Wheatstone. The descriptions are listed under the headings of optics, colour, subjective visual phenomena, motion perception, eye movements, binocular vision, and space perception.
Efficiency of Selective Attention: Selection by Colour and Location Compared
Authors: Laarni Jari , Koski Mika , Nyman Gōte
Published: January 2007

Although we can selectively attend to colour, preknowledge of the location of a target has been shown to facilitate visual selection more than preknowledge of the target colour. Here the effects of peripheral flash cues and central colour cues were compared in three experiments. A novel colour-cuing procedure was used in which the target location was designated in advance by colour. Since variations in stimulus eccentricity and density similarly affected performance in both conditions, the colour cues presumably also made it possible to direct attention quickly to the target location. Thus, the colour cues in this study were analogous to symbolic location cues, such as central digits. Moreover, even though peripheral colour information was provided in experiments 1 and 2 only 84 ms before stimulus array, ie at the same time as the onset cue was flashed on, the effect of colour cues was comparable to that of peripheral flashes. This is a surprising finding given previous data on the time to interpret symbolic location cues and to allocate attention to the target location.
Linear Motion Aftereffect Induced by Pure Relative Motion
Authors: Ashida Hiroshi , Susami Kenji
Published: January 2007

The effect of adaptation to pure relative motion was investigated for the motion aftereffect (MAE) of linear translation motion. In experiment 1, MAE induced by adaptation in the surrounding area was tested. The relative motion signal significantly increased the magnitude of MAE while local MAE in the surrounds was not affected. In experiment 2, MAE observed in the same adapted area was examined while local adaptation was cancelled out. Substantial MAE was found only when the test stimuli included the surroundings, which is considered to be favourable for relative motion mechanisms. These results clearly indicate that MAE is induced by adaptation to pure relative motion as well as by local motion. MAE should be regarded as a composite phenomenon reflecting multiple sites of adaptation including the local and the relative motion levels. The results also provide evidence for the existence of independent detecting mechanisms for relative motion processing.
Orientation Priming of Novel Shapes in the Context of Viewpoint-Dependent Recognition
Authors: Gauthier Isabel , Tarr Michael J
Published: January 2007

Can visual similarity between shapes facilitate orientation priming? Five experiments are reported in which this possibility was explored by using novel two-dimensional shapes that formed homogeneous stimulus classes. After training on individual shapes in a canonical view, the recognition of these shapes was tested in several picture-plane orientations. In experiments 1 and 2 an identification task was used to replicate the classic finding obtained with the mirror-judgment task—that prior orientation cueing does not reduce the magnitude of orientation dependence in processing rotated shapes. The results of experiment 3, however, indicate that blocking trials by orientation is one condition in which orientation priming may be obtained. Experiment 4 builds on this result, and it is suggested that awareness of the blocking manipulation is not required to obtain orientation priming. In experiment 5 the mechanisms underlying this finding are explored, and evidence is offered that orientation priming is a consequence of representations that encode both shape and orientation. Such results may be considered as an extension to the ‘image-based’ approach to object recognition, demonstrating that generalization across exemplars may occur within recognition mechanisms that are viewpoint dependent.
Sex Classification is Better with Three-Dimensional Head Structure Than with Image Intensity Information
Authors: O'Toole Alice J , Vetter Thomas , Troje Nikolaus F , Bülthoff Heinrich H
Published: January 2007

The sex of a face is perhaps its most salient feature. A principal components analysis (PCA) was applied separately to the three-dimensional (3-D) structure and graylevel image (GLI) data from laser-scanned human heads. Individual components from both analyses captured information related to the sex of the face. Notably, single projection coefficients characterized complex differences between the 3-D structure of male and female heads and between male and female GLI maps. In a series of simulations, the quality of the information available in the 3-D head versus GLI data for predicting the sex of the face has been compared. The results indicated that the 3-D head data supported more accurate sex classification than the GLI data, across a range of PCA-compressed (dimensionality-reduced) representations of the heads. This kind of dual face representation can give insight into the nature of the information available to humans for categorizing and remembering faces.
The Influence of Aperture Surfaces on the Barber-Pole Illusion
Authors: Mussap Alexander J , Grotenhuis Kerrie Te
Published: January 2007

The magnitude of the barber-pole illusion is measured as a function of the contrast, orientation, and phase difference between the moving ‘barber-pole’ grating and a moving ‘surround’ grating that forms the aperture surface. It is found that as the difference between the barber-pole grating and the surround grating increases, the influence of surround motion on barber-pole motion decreases (resulting in an increase in the magnitude of the barber-pole illusion). This pattern of results is interpreted as evidence for competition between processes that detect the motion of line terminators along the length of the rectangular aperture and processes that detect grating motion in directions perpendicular to grating orientation.
Facial Distinctiveness and the Power of Caricatures
Authors: Rhodes Gillian , Byatt Graham , Tremewan Tanya , Kennedy Anthony
Published: January 2007

Caricatures, which increase the distinctiveness of faces, are generally recognised at least as well as undistorted images of those faces. However, caricatures seem to facilitate recognition more for some faces than others. An investigation was made into whether the effectiveness of caricaturing depends on a face‘s initial distinctiveness. In experiments 1–3, subjects learned names for unfamiliar faces (photographs) that varied in distinctiveness, and were tested on recognition of caricatures, anticaricatures, and undistorted images of those faces. The test images were line drawings in experiments 1 and 2 and photographic images in experiment 3. Experiments 1 and 2 were identical except that subjects had more exposure to the study photographs in experiment 1. In all three experiments, distinctive faces were recognised (named) more accurately than less-distinctive faces, and caricatures were recognised at least as accurately as undistorted images and better than anticaricatures. However, distinctiveness and caricature level did not interact. Nor did a face's initial distinctiveness correlate with the degree of recognition facilitation produced by caricaturing (experiments 1–3) or with the caricature level chosen as the best likeness (experiment 4). The effectiveness of caricatures varied across faces and experimental conditions, but these differences did not relate to differences in initial distinctiveness. These results prompted a more careful analysis of the expected relationship between initial distinctiveness and the power of caricatures, which indicated that the relationship may be curvilinear rather than linear. In addition, it was found that line-drawing caricatures functioned as superportraits (recognised better than undistorted images—experiment 1) but photographic caricatures did not (experiment 3), suggesting that the forensic potential of caricatures may be limited.
Preschoolers' Perception of other People's Looking: Photographs and Drawings
Authors: Anderson James R , Doherty Martin J
Published: January 2007

Children aged 3–4 years were tested for their ability to decide which of two photographs or drawings of a face depicted the act of fixating on a target object; in each control photograph or drawing the same face and object were present without fixation. Performance was above chance on both stimulus types, but low enough to call into question conclusions from previous research. The same children were also tested on their ability to discriminate between photographs/drawings depicting two faces fixating the same object (joint visual attention) and the same two faces fixating different objects. While discrimination of joint visual attention depicted in drawings was as good as discrimination of fixation in the single-face tasks, the ability to reliably choose between a photograph of two people attending to a common object and a control photograph was significantly poorer. The results suggest that, while young infants and children may be highly sensitive to face-on gaze, even well into the fourth year of life children arc unable consistently to interpret (1) direction of non-self-directed gaze in static faces and (2) joint visual attention by others.
Early-Blind Subjects' Spatial Representation of Manipulatory Space: Exploratory Strategies and Reaction to Change
Authors: Gaunet Florence , Martinez Jean-Luc , Thinus-Blanc Catherine
Published: January 2007

The present study was aimed at analysing the effects of a lack of visual experience in human subjects on the detection and identification of a spatial change brought about to a configuration of objects displayed in manipulatory space. Exploratory patterns and performance levels were recorded. Learning effects were observed in different types of change and condition of presentation only in the early-blind and blindfolded sighted groups, but not in the late-blind group. Early blindness affected both exploratory patterns and performance levels. In addition, significant correlations were found between performance level and the use of systematic patterns of exploration. These data are discussed in relation with the importance of early vision during the development of spatial cognition.
Presentation-Time Measures of the Effects of Manipulations in Colour Space on Discrimination of Famous Faces
Authors: Lee Kieran J , Perrett David
Published: January 2007

Caricaturing the distinctive shape of famous faces can produce an advantage in reactiontime paradigms but the role of distinctive colour and intensity information in recognition of facial identity has not previously been explored. A presentation-time paradigm was developed by which stimuli could be presented for a range of brief display periods. Subjects were required to identify photo-realistic colour representations of famous faces which either were veridical, were caricatured in colour space, or had enhanced colour saturation and intensity contrast (as contrast controls). Recognition accuracy was greater when viewing the caricatured stimuli than either the veridical images or the contrast controls. The removal of colour information to produce grey-scale images also decreased accuracy of face recognition. Both results indicate that colour information aids differentiation of a class of natural stimuli with similar configurations. Thus it is demonstrated that caricaturing faces can be extended to the colour domain and, as with shape caricaturing, enhancement of distinctive information can produce a recognition advantage for famous faces.
The Effects on Bilateral-Symmetry Detection of Multiple Symmetry, near Symmetry, and Axis Orientation
Authors: Wenderoth Peter
Published: January 2007

Palmer and Hemenway (1978 Journal of Experimental Psychology: Human Perception and Performance4 691–702) reported that shapes with multiple axes of symmetry are processed faster than those with single symmetry even when trials are blocked so that the subject knows that any symmetry axis will be vertical. Because their model of symmetry detection postulated a two-stage process in which all orientations are searched crudely at first, in no particular order, followed by second-stage scrutiny, the continued salience of multiple over single symmetry with blocking could not be explained. They claimed that stimuli with multiple axes of symmetry have an additional ‘goodness’.

Four experiments are reported in which it is demonstrated that both sensitivity ( d′) and response bias ( β) vary considerably in symmetry detection, not just as a function of the positive (symmetrical) stimuli used but also as a function of the negative or conjugate instances selected. Although stimuli with multiple axes of symmetry may well have extra salience due to pattern ‘goodness’, this factor may have been confounded with response bias in Palmer and Hemenway's experiments. It is suggested that several of their—as well as other researchers—results could be due to some combination of the effects of type of positive stimulus, type of negative stimulus, and response bias directed towards responding positively to highly symmetrical stimuli in a mix of less symmetrical stimuli. Palmer and Hemenway appear to have been correct in suggesting that subjects are more sensitive to quadruple than single symmetry, but the experiments indicate that subjects are also more willing to respond “symmetrical” to stimuli with quadruple symmetry when trials are not blocked, as in Palmer and Hemenway's experiment 1. However, it is demonstrated that the latter effect can be removed by blocking trials so that only one class of symmetrical pattern and one class of asymmetrical pattern occur in any block.
Spatial Scale Interactions in Stereo Sensitivity and the Neural Representation of Binocular Disparity
Authors: Smallman Harvey S , MacLeod Donald I A
Published: January 2007

How are binocular disparities encoded and represented in the human visual system? An ‘encoding cube’ diagram is introduced to visualise differences between competing models. To distinguish the models experimentally, the depth-increment-detection function (discriminating disparity d from d ± Δ d) was measured as a function of standing disparity ( d) with spatially filtered random-dot stereograms of different centre spatial frequencies. Stereothresholds degraded more quickly as standing disparity was increased with stimuli defined by high rather than low centre spatial frequency. This is consistent with a close correlation between the spatial scale of detection mechanisms and the disparities they process. It is shown that a simple model, where discrimination is limited by the noisy ratio of outputs of three disparity-selective mechanisms at each spatial scale, can account for the data. It is not necessary to invoke a population code for disparity to model the depth-increment-detection function.

This type of encoding scheme implies insensitivity to large interocular phase differences. Might the system have developed a strategy to disambiguate or shift the matches made at fine scales with those made at the coarse scales at large standing disparities? In agreement with Rohaly and Wilson, no evidence was found that this is so. Such a scheme would predict that stereothresholds determined with targets composed of compounds of high and low frequency should be superior to those of either component alone. Although a small stereoacuity benefit was found at small disparities, the more striking result was that stereothresholds for compound-frequency targets were actually degraded at large standing disparities. The results argue against neural shifting of the matching range of fine scales by coarse-scale matches posited by certain stereo models.
Discrimination of Changes in the Slopes of the Amplitude Spectra of Natural Images: Band-Limited Contrast and Psychometric Functions
Authors: Tolhurst David J , Tadmor Yoav
Published: January 2007

Thresholds were measured for discriminating changes in the slopes of the amplitude spectra of stimuli derived from photographs of natural scenes and from random-luminance patterns. The variety and magnitudes of the thresholds could be explained by a model based on the discrimination of the changes in band-limited local contrast. Different spatial scales of local contrast (or different spatial-frequency bands of about 1 octave) were implicated for different reference spectral slopes; the model implicated a lower frequency-band for stimuli with shallower amplitude spectra. The implications of the model were tested experimentally by using stimuli in which the spectra were changed within restricted spatial-frequency bands. When the amplitude spectra of the test and reference stimuli differed only within the implicated frequency bands, thresholds were affected little. However, when the test and reference spectra differed at all frequencies except those in the implicated bands, the thresholds were elevated markedly. The forms of the psychometric functions for the discrimination task were entirely compatible with the hypothesis that the task relies upon the ability to discriminate changes of contrast. The Weibull functions fitted to the data had slope parameters (β) in the range 1 to 3, compatible with discrimination of low (but suprathreshold) contrasts.
Human Cortical-Evoked Fields during Detection, Localisation, and Identification of ‘Pop-out’ Targets
Authors: Saarinen Jukka , Vanni Simo , Hari Riitta
Published: January 2007

We investigated human cortical activity during four ‘effortless-pop-out’ visual search tasks with the use of magnetoencephalography. The search display, which was identical across all the tasks, consisted of vertical line segments, one of which was rotated abruptly 45° clockwise or counterclockwise. In the passive-viewing task the observers gave no response to the search display. In the target-detection task they responded to the onset of the target motion irrespective of its location and direction. In the target-localisation task the observers reported whether the line rotation appeared above or below the fixation point while ignoring the direction of the rotation. In contrast, in the target-identification task they indicated the direction of the line rotation, and the location of the rotation in the array was irrelevant. Cortical activity was recorded with a whole-scalp magnetometer while the observers were performing each task. In addition to the expected activation of the occipital and somatomotor cortical regions, two other active cortical areas were consistently identified in both hemispheres: one in the occipito-temporal area, probably corresponding to the motion-specific V5 complex, and another in the parieto-temporal region. The activation of the right occipito-temporal source depended on the task. The maximum amplitude was smallest for the passive viewing, increased for the detection task, and was largest for the localisation and identification.
On the Relative Salience of Euclidean, Affine, and Topological Structure for 3-D Form Discrimination
Authors: Todd James T , Chen Lin , Norman J Farley
Published: January 2007

A match-to-sample task was performed, in which observers compared configurations of line segments presented stereoscopically in different three-dimensional orientations. Several different structural properties of these configurations were manipulated, including the relative orientations of line segments (a Euclidean property), their coplanarity (an affine property), and their patterns of cointersection (a topological property). Although the differences in these properties to be detected were all metrically equivalent, they varied dramatically in their relative perceptual salience, such that the error rates and reaction times in the three conditions varied by as much as 400%. Performance was highest in the topological condition, intermediate in the affine condition, and lowest in the Euclidean condition. These findings suggest that the relative perceptual salience of object properties may be systematically related to their structural stability under change, in a manner that is similar to the Klein hierarchy of geometries.
Two-Dimensional Representations of the Third Dimension and Their Perception by Infants
Authors: Lécuyer Roger , Durand Karine
Published: January 2007

Many researchers have examined the perception of the third dimension or the preference for three-dimensional versus two-dimensional stimuli in infants, but little is known about infants' representation of the third dimension in a two-dimensional display. Two experiments were conducted to study this capacity. The first experiment was a replication of earlier work, involving a television screen. No difference was observed between looking durations for the ‘normal’ and ‘strange’ events in 4-month-olds. As this situation was cognitively complex, a simpler interposition situation was displayed to 3-month-olds in the second experiment. Infants then looked longer at the ‘strange’ event than at the ‘normal’ event, suggesting that in a complex situation more perceptual indices must be given to infants. These different data are discussed.
Increasing-Loudness Aftereffect following Decreasing-Intensity Adaptation: Spectral Dependence in Interotic and Monotic Testing
Authors: Reinhardt-Rutland Anthony H
Published: January 2007

Listening to decreasing intensity leads to illusory increasing loudness afterwards. Evidence suggests that this increasing-loudness aftereffect may have a sensory component concerned with dynamic localisation. This was tested by comparing the spectral dependence of monotic aftereffect (adapting and testing one ear) with the spectral dependence of interotic aftereffect (adapting one ear and testing the other ear). Existence of the proposed component implies that monotic aftereffect should be more spectrally dependent than interotic aftereffect. Three listeners were exposed to a 1 kHz adapting stimulus. From responses of “growing softer” or “growing louder” to test stimuli changing in intensity, nulls were calculated; test carrier frequencies ranged from 0.5 kHz to 2 kHz. Confirming the hypothesis, monotic aftereffect was about three times as strong as interotic aftereffect for the 1 kHz test carrier frequency, while monotic and interotic aftereffects were comparable in magnitude for test carrier frequencies below about 0.8 kHz and above about 1.2 kHz. The latter residual aftereffects are attributed to cognitive processing, perhaps concerning response bias. Sensitivity did not vary systematically across conditions; this is consistent with evidence that changing intensity entails mainly direct processing. The results cannot be attributed to the loudness adaptation elicited by steady stimuli.
Haptic Underestimation of Angular Extent
Authors: Lakatos Stephen , Marks Lawrence E
Published: January 2007

To what extent can individuals accurately estimate the angle between two surfaces through touch alone, and how does tactile judgment compare to visual judgment? Subjects' ability to estimate angle size for a variety of haptic and visual stimuli was examined in a series of nine experiments. Triangular wooden blocks and raised contour outlines comprising different angles and radii of curvature at the apex were used in experiments 1 – 4 and it was found that subjects consistently underestimated angular extent relative to visual baselines and that the degree of underestimation was inversely related to the actual size of the angle. Angle estimates also increased with increasing radius of curvature when actual angle size was held constant. In contrast, experiments 5–8 showed that subjects did not underestimate angular extent when asked to perform a haptic – visual match to a computerized visual image; this outcome suggests that visual input may ‘recalibrate’ the haptic system's internal metric for estimating angle. The basis of this crossmodal interaction was investigated in experiment 9 by varying the nature and extent of visual cues available in haptic estimation tasks. The addition of visual-spatial cues did not significantly reduce the magnitude of haptic underestimation. The experiments as a whole indicate that haptic underestimations of angle occur in a number of different stimulus contexts, but leave open the question of exactly what type of visual information may serve to recalibrate touch in this regard.
Picturing Peripheral Acuity
Authors: Anstis Stuart
Published: January 2007

The grain of the retina becomes progressively coarser from the fovea to the periphery. This is caused by the decreasing number of retinal receptive fields and decreasing amount of cortex devoted to each degree of visual field (= cortical magnification factor) as one goes into the periphery. We simulate this with a picture that is progressively blurred towards its edges; when strictly fixated at its centre it looks equally sharp all over.
Visual Search of Driving Situations: Danger and Experience
Authors: Chapman Peter R , Underwood Geoffrey
Published: January 2007

Previous research on visual search in driving suffers from a number of problems: small sample sizes, a concentration on mundane situations, and a failure to link results to more general psychological theory. The study reported in this paper addresses these issues by recording the eye movements of a large sample of drivers while they watched films of dangerous driving situations and comparing the findings with those from more general studies on scene perception. Stimuli were classified according to the types of road shown and the degree of danger present in the scenes. Two groups of subjects took part, fifty-one young novice drivers who had just gained a full driving licence and twenty-six older more experienced drivers. Dangerous situations were characterised by a narrowing of visual search, shown by an increase in fixation durations, a decrease in saccade angular distances, and a reduction in the variance of fixation locations. These effects are similar to the concept of ‘attention focusing’ in traumatic situations as it is described in the literature on eyewitness memory. When road types are compared, the least visually complex rural roads attracted the longest fixation durations and the shortest angular saccade distances, while the most visually complex urban roads attracted the greatest spread of search but the shortest fixation durations. Differences between the groups of subjects were also present. Novices had longer fixation durations than experienced drivers, particularly in dangerous situations. Experienced drivers also fixated lower down and had less vertical variance in fixation locations than novices.
Inattentional Blindness as a Function of Proximity to the Focus of Attention
Authors: Newby Ethan A , Rock Irvin
Published: January 2007

The effect of the distance between the center of the focus of attention and an unexpected stimulus on detection was examined in two experiments with the use of the inattentional-blindness paradigm [Mack and Rock, 1998 Inattentional Blindness (Cambridge, MA: MIT Press)]. In experiment 1, the closer a stimulus was to the center of attention, the more likely it was to be detected. Experiment 2 replicated this finding and controlled for retinal eccentricity. These results suggest that low-level stimulus characteristics (eg location) may play an important role in the detection of unexpected stimuli. The data are consistent with previous research on the spatial aspects of attention demonstrating that the distance to the focus of attention is a critical variable. This study demonstrates that the effect of distance is similar under conditions of inattention. Theories put forward to explain inattentional blindness should include ‘early’ attentional factors, as well as factors resulting from later stages of processing.
Perceived Object Shape Affects the Perceived Direction of Self-Movement
Authors: Beusmans Jack M H
Published: January 2007

The ‘direct-perception’ model of heading perception posits that heading is computed directly from optic flow without an intervening structural representation of environmental layout. Here, I give an example in which such a representation is seen to play a role in the interpretation of optic flow. Manipulating the outline of concave objects to give an erroneous percept of convexity caused the perceived direction of heading during a simulated approach to change as well. Thus, the representation of environmental structure provides the context for using and interpreting image motion.
Effects of Collimation on Perceived Layout in 3-D Scenes
Authors: Andersen George J , Saidpour Asad , Braunstein Myron L
Published: January 2007

The effect of varying information for overall depth in a simulated 3-D scene on the perceived layout of objects in the scene was investigated in two experiments. Subjects were presented with displays simulating textured surfaces receded in depth. Pairs of markers were positioned at equal intervals within the scenes. The subject's task was to judge the depth between the intervals. Overall scene depth was varied by viewing through either a collimating lens or a glass disk. Judged depth for equal depth intervals decreased with increasing distance of the interval from the front of the scene. Judged depth was greater for collimated than for non-collimated viewing. Interestingly, collimated viewing resulted in a uniform rescaling of the perceived depth intervals.
Viewer-Centered Temporal Biasing of 3-D Rotation Percepts
Authors: Pantle Allan J , Papp Robert J , Reynolds Samuel J , Cubells Olga L , Gallogly Donald P
Published: January 2007

The perceived direction of rotation of a 3-D cloud of dots can be biased by a prior rotation (Jiang, Pantle, and Mark, 1998 Perception & Psychophysics 60 275–286). In a series of experiments, it is shown that the temporal rotation bias is reversed by a 180° change of head orientation between two rotation sequences; ie the perceived direction of rotation reverses for the second of two sequences when head orientation is changed. The bias is, therefore, viewer-centered. Perceptual reversals are not obtained when the orientation of the head is changed and returned to its original position between rotation sequences. It was also found that the viewer-centered bias combined additively with viewer-independent near-far luminance information. Finally, the bias was manifest when 3-D depth was re-established, but not maintained, between rotation sequences. A model, in descriptive and flowchart forms, is used to explain the integration of world-centered information and a viewer-centered temporal bias on the presence/absence of perceptual reversals of the rotating virtual sphere. In the model, the temporal bias is the result of the coupling of depth values to persisting 2-D retinal motion signals.
The Line-Motion Illusion Can Be Reversed by Motion Signals after the Line Disappears
Authors: Eagleman David M , Sejnowski Terrence J
Published: January 2007

In the line-motion illusion, a briefly flashed line appears to propagate from the locus of attention, despite being physically presented on the screen all at once. It has been proposed that the illusion reflects low-level visual information processing that occurs faster at the locus of attention (Hikosaka et al 1993 Vision Research33 1219–1240; Perception22 517–526). Such an explanation implicitly embeds the assumption that speeding or slowing of neural signals will map directly onto perceptual timing. This ‘online’ hypothesis presupposes that signals which arrive first are perceived first. However, other evidence suggests that events in a window of time after the disappearance of a visual stimulus can influence the brain's interpretation of that stimulus (Eagleman and Sejnowski 2000 Science287 2036–2038; 289 1107a; 290 1051a; 2002 Trends in Neuroscience25 293). If the online hypothesis were true, we should expect that events occurring after the flashing of the line would not change the illusion. Consistent with our hypothesis that awareness is an a posteriori reconstruction, we demonstrate that the perceived direction of illusory line-motion can be reversed by manipulating stimuli after the line has disappeared.