bluuebunny/crossref_metadata_2025 huggingface dataset:
How Faces Differ—A New Comparative Technique
Authors: Haig Nigel D
Published: January 2007

It can be argued that the process of recognising faces progresses in two stages: first, the realisation that a perceived image contains patterns that may most reasonably be interpreted as forming a discrete face; second, correct and positive identification by noting the particular features that differentiate one face from all others. A novel technique which explored the latter process in the particular case of four different (male) faces is described. The experiment took the form of a four-alternatives forced-choice presentation of faces behind masks which contained a number of randomly positioned apertures. The percentage of correct responses for each separate aperture was then computed after a large number of 1 s presentations to four observers. This novel form of experiment suggested an equally novel form of pictorial data presentation that, literally, highlights the salient features of each individual face and thereby allows detailed intercomparison merely by inspection. Summing over all targets and observers reveals a strong preference for eyes and eyebrows, followed closely by the hairline above the temples. Next in order of preference comes the mouth and upper-lip area, followed by the lateral hairline beside each temple. Individual differences are strong, however, and the variations are such as to suggest that the uncritical application of generalised feature saliency lists is neither useful nor appropriate.
Perceptual Organization and Apparent Brightness in Subjective Contour Figures
Authors: Bradley Drake R , Mates Steven M
Published: January 2007

According to a number of theories subjective contours arise from brightness contrast and/or assimilation. The apparent brightness gradients generated by these effects are assumed to give rise to the perception of contours delineating the gradients. A study is reported in which naive observers were shown a subjective contour display and asked to report what they saw. They were then asked to judge whether the center or the surround of the display appeared brighter. Subjects whose reports indicated that they had seen the subjective contour figure showed an overwhelming preference for the center of the display being brighter than the surround. However, subjects who did not see the subjective contour figure did not differ significantly in their selection of the center over the surround. This finding presents difficulties for any theory which derives subjective contours from the apparent brightness difference.
What Variables Control (Long-Range) Apparent Motion?
Authors: Prazdny Kvetoslav
Published: January 2007

A solid (ie filled-in) two-dimensional form is seen in motion toward another solid object of different shape and not towards an outline object of the same shape. The interpretation of these findings in terms of luminance-domain spatial frequency filtering is challenged by experiments in which the same results were obtained with kinetic and cyclopean forms.
Static Depiction of Movement
Authors: Carello Claudia , Rosenblum Lawrence , Grosofsky Alexis
Published: January 2007

A number of pictorial devices were compared in order to assess their relative effectiveness in depicting events. Effectiveness, as measured by a rating task, did not seem to be a function of the classification of a device as natural or metaphorical. Rather, it depended on whether a given device highlighted a distinctive aspect of a particular event (running, jumping, or moving), or simply modified the event. This observation was buttressed by the existence in a forced-choice task of a category boundary for depictions of running (pictures with a certain device were seen as running, those without it were not) but not for moving or jumping. Even preschool children displayed some understanding of metaphorical devices. They chose figures with those devices as running faster than the experimental standard. Results are discussed in the context of Kennedy's characterization of pictorial metaphors and Gibson's framework for understanding the relationship between pictorial and environmental information.
Hemifield Differences in Perceived Velocity
Authors: Smith Andrew T , Hammond Peter
Published: January 2007

Measurements of the perceived velocity of a drifting grating were obtained as a function of the position of the grating in the visual field. Identical drifting gratings were presented at the same eccentricity in the left, right, upper, and lower hemifields, and the perceived velocities were compared. A group of ten subjects considered together showed no significant hemifield differences in perceived velocity. However, some individual subjects showed marked and systematic hemifield differences, the directions of which varied among the subjects. There were no hemifield differences in susceptibility to adaptation to moving gratings.
Induced Motion Considered as a Visually Induced Oculogyral Illusion
Authors: Post Robert B
Published: January 2007

The possibility that nystagmus suppression contributes to illusory motion was investigated by measuring perceived motion of a stationary stimulus following the removal of an optokinetic stimulus. This was done because optokinetic nystagmus typically outlasts cessation of an optokinetic stimulus. Therefore, it would be expected that a stationary fixated stimulus should appear to move after removal of an optokinetic stimulus if illusory motion results from nystagmus suppression. Illusory motion was reported for a stationary fixation target following optokinetic stimulation. This motion was reported first in the same direction as the preceding induced motion, then in the opposite direction. The two directions of illusory motion following optokinetic stimulation are interpreted as resulting from the use of smooth ocular pursuit to suppress first one phase of optokinetic afternystagmus and then the reverse phase. Implications for the origins of induced motion are discussed.
Is There Anything out There?: A Study of Distal Attribution in Response to Vibrotactile Stimulation
Authors: Epstein William , Hughes Barry , Schneider Sandra , Bach-Y-Rita Paul
Published: January 2007

Patterns of vibrotactile stimulation were delivered to the index fingertips of naive blindfolded subjects. The attributions made by these subjects when they were allowed to experience transformations of vibrotactile stimulation correlated with self-movement were assessed. Although the subjects became aware of the relationship between self-movement and stimulation transformation, they never developed the hypothesis of distal attribution, ie the hypothesis that the ultimate cause of their vibrotactile experience was an encounter with an object in the environment. It is proposed that further investigations of the course of acquisition of distal attribution in the situation described may be instructive in the study of externalization in other modalities.
Tactile Recognition of Laterally Inverted Mirror Images by Children: Intermanual Transfer and Rotation of the Palm
Authors: Römer Gisela , Gresch Heike , Ettlinger George , Brown Josephine V
Published: January 2007

Intermanual tactile recognition of laterally inverted mirror shapes was studied, with special reference to the role of the thumb. Children were allowed to feel the shapes either with the whole hand, with only four fingers (excluding the thumb), or with only the index finger. Intramanual recognition was also studied after rotation of the hand from the palm down/up to the palm up/down orientation. The thumb was found not to be important for intermanual mirror reversals, and only of limited importance for intramanual reversals. There was no evidence that coding with reference to the hand is of importance for either inter- or intramanual reversals. The explanations for the two kinds of reversals are quite different.
Apparent Height of a Stereokinetic Cone is Decreased by Departure from Circularity
Authors: Wilson John A , Robinson James O , Piggins David J
Published: January 2007

Subjects made judgements of the comparative height of the stereokinetic cones seen for pairs of rotating figures with varying eccentricity and ellipticity. For any given eccentricity, ellipticity of the figure reduced the apparent height, with narrow ellipses seeming to be shallower. The effect is attributed to an interaction in constancy scaling.
The Effect of Line-Figure Information on the Magnitude of the Dot Forms of the Poggendorff and Müller-Lyer Illusions
Authors: Predebon John
Published: January 2007

The magnitudes of the dot and line forms of the Poggendorff illusion and the Brentano version of the Müller-Lyer illusion were assessed in two groups of subjects: the informed group was given information about the implied figure configuration in the dot pattern, the uninformed group was not. The informed group produced a significantly greater dot illusion than the uninformed group, and there was no difference between the two groups in the magnitudes of the line illusions. The experiments are discussed in the context of Coren and Porac's proposal that illusion-inducing mechanisms can be divided into structural and cognitive components. The results suggest that about 64% of the magnitude of the Poggendorff illusion and about 54% of the Müller-Lyer illusion can be attributed to the involvement of cognitive factors.
Surface Contours, Glass Patterns, and a Slant Illusion
Authors: Earle David C
Published: January 2007

A surface contour pattern constructed from continuous sine waves is subject to several visual interpretations, whereby the separate regions containing the maxima and the minima of the sine waves may be seen as representing either convex or concave areas of a three-dimensional surface. In a pattern of segments of contours comprising only the regions containing the maxima and minima of the sine waves, a set of surfaces is perceived, each of which tends to be seen as convex, and which possesses an illusory slant which is different for columns of contour segments containing maxima as compared with columns containing minima. It is conjectured that the slant illusion is a manifestation of the processes by which depth is derived from surface contour information. It is demonstrated that corresponding figures constructed from sinusoidal Glass patterns produce similar effects. From this it is concluded that the structure of Glass patterns provides a sufficient input representation for the processes by which surface shape is recovered from surface contours.
Similarity of Normalized Discrimination Ellipses in the Constant-Luminance Chromaticity Plane
Authors: Boynton Robert M , Nagy Allen L , Eskew Rhea T
Published: January 2007

Discrimination steps were measured for three subjects, along oblique axes passing through nine points in a 25 td constant-luminance chromaticity plane. When plotted in a normalized cone-excitation chromaticity diagram, the best-fitting discrimination ellipses for a given subject have approximately the same shape and orientation regardless of the reference chromaticity. Their orientation is consistent with the hypothesis that excitation of B-cones affects the red—green opponent balance, otherwise determined by R- and G-cone excitations, in a manner independent of initial cone-excitation levels. The CIELAB formula predicts an orientation for normalized ellipses in agreement with the data, but it also predicts systematic changes in the ratio of minor to major axes which are not observed experimentally.
The Goldmeier Effect in Adults and Children: Environmental, Retinal, and Phenomenal Influences on Judgments of Visual Symmetry
Authors: Fisher Celia B , Fracasso Maria P
Published: January 2007

Adults judge that patterns symmetrical about the vertical axis are more similar to standard patterns symmetrical about both major orthogonal axes than are patterns which are symmetrical only about the horizontal axis (the Goldmeier effect). Thus, symmetry about the vertical axis is more salient for adults than symmetry about the horizontal axis. Two experiments are reported in which subjects from three age groups (preschool, 8 years old, and adult) were given Goldmeier problems under different conditions. In experiment 1 three head-tilt conditions were used (0°, 45°, 90°); in experiment 2 there were four conditions defined by head orientation (0°, 90°) and phenomenal instructions (top of figure at 0° or at 90°). In both experiments, increasing head tilt from 0° decreased the consistency with which the environmentally vertical pattern was chosen. Noncorrespondence between the three spatial frameworks (environmental, retinal, and phenomenal) failed to produce biases in favor of either retinal-egocentric or phenomenal systems. For rotated adult subjects in experiment 2, 0° phenomenal instructions strengthened an environmental bias, and 90° phenomenal instructions shifted responses toward a retinal bias. These findings provide strong refutation of explanations for symmetry perception that are based solely upon the anatomical symmetry of the visual system. The data also fail to support arguments for environmental or phenomenal frameworks as singular influences. The results are best explained in terms of failure of constancy mechanisms to coordinate environmental and retinal information as a function of degree of head rotation and stimulus complexity.
Sensitivity to Changes in Size and Velocity in Young and Elderly Observers
Authors: Brown Brian , Bowman Kenneth J
Published: January 2007

Thresholds for detection of change of size and for detection of change of velocity were measured in young and elderly observers. No differences in thresholds between these subject groups were found at the fovea or in more peripheral retina. The results indicate a degree of functional redundancy in the peripheral retina of elderly subjects, even though there is evidence of reduced numbers of functional photoreceptors in the periphery.
The Representation of Uniform Motion in Vision
Authors: Swanston Michael T , Wade Nicholas J , Day Ross H
Published: January 2007

For veridical detection of object motion any moving detecting system must allocate motion appropriately between itself and objects in space. A model for such allocation is developed for simplified situations (points of light in uniform motion in a frontoparallel plane). It is proposed that motion of objects is registered and represented successively at four levels within frames of reference that are defined by the detectors themselves or by their movements. The four levels are referred to as retinocentric, orbitocentric, egocentric, and geocentric. Thus the retinocentric signal is combined with that for eye rotation to give an orbitocentric signal, and the left and right orbitocentric signals are combined to give an egocentric representation. Up to the egocentric level, motion representation is angular rather than three-dimensional. The egocentric signal is combined with signals for head and body movement and for egocentric distance to give a geocentric representation. It is argued that although motion perception is always geocentric, relevant registrations also occur at the three earlier levels. The model is applied to various veridical and nonveridical motion phenomena.
Pseudoscopic Viewing: Transfer and Persistence of Reversed Depth Relations from the Viewing of Photographs to the Real Scene
Authors: Kalaugher Patrick G
Published: January 2007

After viewing stereo pictures pseudoscopically (that is, with the pictures of the stereo-pair presented to the opposite eyes) part of the real scene depicted was perceived as inside out from the standpoint of depth during normal binocular vision. Experiments were designed to investigate this form of transfer but, since serious consequences can arise when an inside-out percept persists in normal binocular vision, it was intended that the experiments would be restricted to transfer of a less extreme kind. The scene chosen had not developed persistence during early trials but, surprisingly, one subject taking part in these experiments did experience some transfer from pseudoscopic direct viewing to normal binocular vision.
Spatial Factors in Visual Attention: Some Compensatory Effects of Location and Time of Arrival of Nontargets
Authors: Gathercole Susan E , Broadbent Donald E
Published: January 2007

It is well established that the identity of nontarget events may affect reaction to a target event, but that spatial separation between the two will reduce such an influence. Two experiments are reported in which an attempt was made to distinguish between two accounts of this effect. On one, some of the information about events spatially distant from the target is shut out from analysis altogether. On the other, such events are fully analysed, but either the analysis proceeds more slowly or else it starts only after a delay. In the experiments the time of arrival of, and the distance between, the target and nontarget events were systematically varied. The conventional effects of the distance of nontargets from target were greatly reduced when the target and nontarget events were asynchronous. If the nontargets arrived first, they had an effect on reaction to the target whether they were near to or far from it. If they arrived second, their identity had no effect at either separation. These results appear to rule out any simple view of attention according to which information outside the target region is denied analysis. Rather, distant nontarget events are analysed, but produce their effects at a later time than less peripheral events.
A Model of Empty Duration Perception
Authors: Nakajima Yoshitaka
Published: January 2007

An attempt to construct a general theory of duration perception is presented. First, four experiments are reported in which the supplement hypothesis, on the relation between two or three empty durations, was examined: the subjective duration of a subjectively empty time interval is directly proportional to its physical duration plus a constant of ~ 80 ms. This hypothesis could be applied to the ratio judgments of auditorily marked empty durations between 40 and 600 ms given serially. It could also explain the discrepancies between musically notated rhythms and the corresponding physical performed rhythms in very simple rhythm patterns consisting of three tones. Next, three earlier experiments on discriminations of empty durations marked by sound bursts were also reanalyzed. Within the range 40–600 ms, the absolute just noticeable difference of an empty duration was almost directly proportional to the standard duration plus a constant of about 80 ms. If the supplement hypothesis is accepted, this means that the relative just noticeable difference of the subjective duration was constant. Finally, the processing time hypothesis is presented: subjective duration is directly proportional to the physical time required to process the given empty duration. This processing is considered to begin with the detection of the first marker, and to end ~ 80 ms after the detection of the second marker.
On the Late Invention of the Stereoscope
Authors: Wade Nicholas J
Published: January 2007

It was not until 1838, when Wheatstone published his account of the stereoscope, that stereoscopic depth perception entered into the body of binocular phenomena. It is argued that the stereoscope was not invented earlier because the phenomenon of stereopsis based on disparity had not been adequately described. This was the case despite the fact that there had been earlier descriptions of tasks that could be performed better with two eyes than with one; the perceptual deficits attendant upon the loss of one eye had been remarked upon; analyses of the projections to each eye were commonplace, and binocular disparities were accurately illustrated; moreover, binocular microscopes and telescopes had been made over a century earlier. Theories of binocular vision were generally confined to accounting for singleness of vision with two eyes, and the concepts employed to account for this were visible direction, corresponding retinal points, and union in the brain. The application of these concepts inhibited any consideration of disparities, other than for yielding diplopia. When perception of the third dimension was addressed by Berkeley at the beginning of the eighteenth century, it was in the context of monocular vision and binocular convergence. Thereafter visual direction became the province for binocular vision and it was analysed in terms of geometrical optics, whereas visual distance was examined in the context of learned associations between vision and touch. This artificial division was challenged initially with respect to visual direction and later with respect to stereopsis. An additional factor delaying the invention of the stereoscope was that experiments on binocular vision generally involved abnormal convergence on extended objects. Wheatstone's accidental observation of stereopsis was under artificial conditions in which disparity alone defined the binocular depth perceived. Once invented the stereoscope was enthusiastically embraced by students of vision. It is suggested that the ease with which retinal disparity could be manipulated in stereopairs has led to an exaggeration of its importance in space perception.
On a Changing Perspective Illusion within Vermeer's The Music Lesson
Authors: Deręgowski Jan B , Parker Denis M
Published: January 2007

The effect of line of sight on the perception of spatial configuration has been investigated in a well-known painting ( The Music Lesson by Vermeer) and in two control patterns. In experiment 1, subjects indicated the perceived inclination of two major contours which defined the sidewall—floor and backwall—floor joints in (i) a projected image of the painting, (ii) a three-line representation of the major spatial elements of the painting, and (iii) a three-dimensional wire model of these same contours, when standing in each of eighteen positions on a line running parallel to the surface of the screen. Results indicated a significant change in the perception of the sidewall—floor, but not of the backwall—floor contour, as viewing angle changed, in both the painting and the three-line representation. However, the angular setting in the latter case was significantly less than when the painting was used, ie subjects underestimated the depicted inclination. Settings for the wire model did not deviate with viewing angle and reflected geometrically correct adjustments. In experiment 2, the results of experiment 1 were confirmed using enantiomorphs. These findings are discussed in the light of other view-dependent illusions in paintings.
The Differential Effects of Brief Exposures and Surrounding Contours on Direct and Indirect Tilt Illusions
Authors: Wenderoth Peter , Johnstone Syren
Published: January 2007

Four experiments in which logarithmic intervals between 25 and 1600 ms were used for stimulus duration in tests for the tilt illusion are reported. It is demonstrated that the direct and the indirect tilt illusions both increase in magnitude inversely with length of stimulus presentation. The data suggest that whereas the direct effect peaks with a value of about +7° at the shortest flash duration used (25 ms), peak indirect effects (of about +2°) do not occur at this duration. In addition, whereas direct effects level out after 100 ms stimulus exposure times, to the usual magnitude obtained with long presentations (about + 2°), indirect effects reach their standard magnitude (−0.5° to −1.0°) later, at exposures of about 400 ms. Even at very short flash durations, a luminance square frame surrounding the illusion display reduces the indirect effect by two thirds of its magnitude but has no effect at all on the direct effect. It is suggested that direct effects arise early in visual processing, in area V1, where there are transient mechanisms and where corruption of orientation analysis by the inducing grating would occur prior to later, extrastriate, global analysis of the surrounding peripheral frame. Indirect effects, on the other hand, may arise later, along the sustained parvocellular colour—form pathway, where more global processing occurs and susceptibility to surrounding fields might be expected.
Uniform-Field Flicker Masking in Control and Specifically-Disabled Readers
Authors: Martin Frances , Lovegrove William J
Published: January 2007

Possible transient-system deficiencies in subjects with specific reading disabilities (SRDs) were investigated in groups of 13-year-old SRDs and control normal readers. In experiment 1, in which a 6 Hz uniform-field flicker (UFF) mask and a stationary test stimulus were used, it was found that the overall effect of UFF masking was to reduce differences in contrast sensitivity between SRDs and normal readers. In experiments 2a and 2b, with UFF masks of 6 and 20 Hz and a 6 Hz moving (experiment 2a) or flickering (experiment 2b) test stimulus, contrast sensitivity in both groups was decreased in the presence of the 6 Hz UFF mask. Only the control group, however, showed a further decrease in sensitivity with the 20 Hz UFF mask. This indicates that the groups differ in terms of a mechanism sensitive to high temporal frequencies. A 20 Hz counterphase flickering test stimulus was used in experiment 3 in the presence of 6 Hz UFF, and it was found that SRDs are less sensitive than controls to 20 Hz flicker across all spatial frequencies used. The 6 Hz mask, however, did not differentially affect the two groups. These findings provide further evidence for a transient-system deficit in the visual systems of SRDs, but also suggest a more complex situation by showing that the two groups differ in a high-temporal-frequency mechanism.
Points and Endpoints: A Size/Spacing Constraint for Dot Grouping
Authors: Zucker Steven W , Davis Sheldon
Published: January 2007

One-dimensional arrangements of dots immediately group into contours. It is reported that, when these contours participate in certain larger arrangements, there is an abrupt point at which the percept changes as a function of dot spacing (or density along the contour). Closely spaced arrangements give rise to subjective effects involving apparent brightness and depth, whereas sparsely spaced ones do not. The effects are most clear in configurations that involve endpoints and possible occlusions. For these configurations, densely dotted contours are perceptually equivalent to solid ones, but sparse ones are not. This change in percept occurs abruptly and consistently at a dot to space ratio of 1:5, when the dot density is normalized by dot size, and this point is called the size/spacing constraint. It holds only for dots of the order of 1 min visual angle in diameter when small to modest contrast values are used. The subjective effects are not present for dotted contours (or even for solid ones) that are smaller (<0.5 min), and differ for contours that are larger (> 10 min). To demonstrate the significance of size/spacing constraints for early vision, a framework for grouping consisting of processes at many different levels is outlined, and the requirements for the earliest one (orientation selection) are sketched in greater detail. The size/spacing constraint follows directly from one of these requirements—receptive field structure—and seems to indicate a switch from early orientation-selection processes to later ones.
The Discrimination of Human Odour by the Dog
Authors: Hepper Peter G
Published: January 2007

In reply to a suggestion made by Galton in 1875, the ability of dogs to discriminate between the odour of human twins was investigated. In a matching-to-sample simultaneous discrimination task, dogs were tested on their ability to discriminate odours from twins differing only in genetic relatedness or only in environmental factors, particularly diet, or from twins identical in both genetic relatedness and environmental factors. Dogs could discriminate between the odours from twins who differed only in environmental factors and between the odours of twins who differed only in genetic relatedness. However, they were unable to discriminate between odours produced by infant twins identical in both genetic relatedness and environmental factors. Thus twins may be discriminated by dogs as long as they differ in genetic relatedness or environmental factors. The possible source of discriminable odours is discussed and how the effects of genes and environment are mediated considered.
Accommodation and Apparent Distance
Authors: Fisher S Kay , Ciuffreda Kenneth J
Published: January 2007

The ability to judge egocentric distance was assessed in sixteen normal observers under conditions where monocular blur-driven accommodation provided the only source of information regarding changes in target dioptric distance. Accommodation and apparent distance were measured over an optical range of 2 to 6 D for each of three targets which differed in their effectiveness as accommodative stimuli (excellent, moderate, and poor). For the excellent and moderate accommodative targets, apparent distance decreased as accommodation increased, with both targets sharing a common linear function. Apparent distance, however, tended to exceed accommodative distance and was relatively compressed in scale. As expected, accommodative response and apparent distance diminished in range as target effectiveness was reduced. The poor accommodative target represented the limiting case wherein accommodation failed to deviate from the tonic level, and apparent distance remained constant. There were considerable intersubject differences in the ability to judge distances on the basis of accommodation. The results indicate that accommodation can indeed serve as a source of distance information, particularly for some individuals.
Left—Right Visual Field Asymmetry in Bistable Motion Perception
Authors: Casco Clara , Spinelli Donatella
Published: January 2007

Twelve observers viewed two alternating frames, each consisting of three rectangular bars which were displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three elements moving as a whole (group movement), whereas with IFIs shorter than 40–60 ms the overlapping elements in each frame appeared stationary while the third element appeared to move from one end of the display to the other (end-to-end movement). The percentage of group movement responses in central viewing was compared to those obtained for stimulus presentation in the left and right visual fields (4 deg eccentricity), for opposite horizontal directions of motion. All ten right-handed subjects showed a left-field advantage in sensitivity to group movement. The two left-handed subjects showed a similar advantage in sensitivity with right-field presentation. The effects of monocular vision, hand used in the task, spatial frequency, and contrast on visual field asymmetry were all investigated in two right-handed subjects. None of these factors affected the left—right asymmetry.
A Simple Analogue Teaching Device for Demonstrating Visual-Receptive-Field Properties
Authors: Moulden Bernard , Martin David
Published: January 2007

A cheap (under £100 at current prices) and simple analogue device is described which permits one to demonstrate, according to an adjustable configuration of the photoreceptive elements, some of the main properties of (i) circularly-symmetrical, (ii) ‘simple’ elongated opponent-flank, and (iii) multiple-discharge-centre visual receptive fields. The design and construction of the device are described, together with some suggested demonstrations.
Vertical Gaze Direction and the Resting Posture of the Eyes
Authors: Heuer Herbert , Owens D Alfred
Published: January 2007

With horizontal gaze, the resting posture of binocular vergence typically corresponds to a distance of about 1 m. The effect of vertical direction of gaze on this basic resting posture was investigated. The dark vergence of twenty-four subjects was measured while they fixated a dim monocular light-point at vertical directions ranging from −45° (lowered) to +30° (elevated). In one condition, gaze was varied by changes in eye position with the head held upright; in a second condition, gaze was varied by changes in head inclination with the eyes held in constant (horizontal) position with respect to the head. In both conditions, dark vergence shifted in the convergent (nearer) direction with lowered gaze and in the divergent (farther) direction with elevated gaze. The effect of varied eye inclination was larger, more variable across subjects, and more stable over time than that of varied head inclination. These findings indicate that multiple mechanisms contribute to gaze-related variations of the resting posture of the eyes. They may help to explain the variations of space perception and visual fatigue that are observed with different gaze inclinations.
Effects of Room Reflectance and Background Noise on Perceived Auditory Distance
Authors: Mershon Donald H , Ballenger William L , Little Alex D , McMurtry Patrick L , Buchanan Judith L
Published: January 2007

Perceptions of egocentric auditory distance were investigated within an environment for which the reverberation time could be systematically varied without changes in the size or shape of the room. Two levels of wide-band background noise, differing by 20 dB, were used as a masking stimulus. Target sounds were presented from distances between 0.75 and 6.0 m and verbal reports of distance were collected from 288 listeners in two separate experiments. Changes in physical distance produced variation in reported distance in each configuration. Reported distance was generally proportional to real distance, but considerably underestimated when room reflectance was low. When room reflectance was high ( T60 ≈ 1.7 s for the range of frequencies used), initial reports of distance were often overestimates; upon repeated presentation, judgments in the high reflectance room became more nearly veridical. The effect of increasing the background noise level was to decrease the perceived distance. These findings are in accord with expectations based upon the importance of reverberation cue(s) to distance and upon previous analyses from this laboratory.
Figure and Ground in Space and Time: 1. Temporal Response Surfaces of Perceptual Organization
Authors: Klymenko Victor , Weisstein Naomi
Published: January 2007

The figure – ground organization of an ambiguous bipartite pattern can be manipulated by altering the temporal-frequency content of the two regions of the pattern. Ambiguous patterns in which the two regions of each pattern contained sine-wave gratings of either 8, 4, 1, or 0.5 cycles deg−1 undergoing contrast reversal at rates of 0, 3.75, 7.5, or 15 Hz were tested for figure–ground organization under conditions of equated space-averaged and time-averaged luminance and perceived contrast. All combinations of temporal-frequency differences between the two regions were tested at each spatial frequency. The data are reported for two levels of temporal resolution (15 and 30 s). The pattern region with the relatively higher temporal frequency tended to be seen as the background a higher percentage of the viewing time. There were significant linear trends for the appearance as background of the region of higher temporal frequency with respect to the magnitude of the temporal-frequency difference between the two regions of each pattern for all spatial frequencies and data intervals except the final 15 s interval of the lowest (0.5 cycle deg−1) spatial-frequency condition.
Figure and Ground in Space and Time: 2. Frequency, Velocity, and Perceptual Organization
Authors: Klymenko Victor , Weisstein Naomi
Published: January 2007

The figure – ground organization of an ambiguous bipartite pattern in which the two regions of the pattern contained sine-wave gratings which differed in spatial frequency was examined for two pairs of spatial frequencies: 1 and 4 cycles deg−1, and 1 and 8 cycles deg−1. The region of higher spatial frequency underwent contrast reversal at one of four rates: 0, 3.75, 7.5, or 15 Hz. The region of lower spatial frequency was equated with either the temporal frequency or the velocity of the grating of higher spatial frequency in three sets of conditions: one stationary condition, three in which temporal frequency was equated, and three in which velocity was equated. For the 1 and 4 cycles deg−1 pair, the region of lower spatial frequency tended to be seen as the background a higher percentage of the time. There were significant linear trends for the appearance as background of the region of lower spatial frequency with respect to the magnitude of the velocity difference between the two regions of the pattern. The faster the 1 cycle deg−1 grating moved with respect to the 4 cycles deg−1 grating, the higher the percentage of the time it was seen as the ground. The results for the 1 and 8 cycles deg−1 pair were in some cases unexpected in that the 8 cycles deg−1 grating was seen as the ground behind the 1 cycle deg−1 grating even though it was of a higher spatial frequency and moved at a slower velocity. The spatiotemporal tuning of the visual system is discussed.
Selection of Reference Frames and the ‘Vicariance’ of Perceptual Systems
Authors: Marendaz Christian
Published: January 2007

Interindividual differences in field dependence—independence (FDI) which emerge in situations of vision—posture conflict when subjects are required to orient their bodies vertically were investigated. The first aim was to see whether the same interindividual differences are found in judgements of the orientation of forms in focal vision in which subjects have to deal with conflicting spatial references processed by different sensory modalities. The second aim was to test the idea that the FDI dimension is due to functional habits linked to balancing. Subjects performed Kopfermann's (1930) shape-orientation task in either a stable (experiment 1) or an unstable (experiment 2) postural condition. Results showed that the FDI dimension comes into play in the solution of the Kopfermann shape orientation task, and that there is an interactive link between FDI and postural balance, consistent with theoretical expectations. More generally, it appears that the ‘choice’ of a spatial reference system is the product of both individual and situational characteristics, and that the ‘vicariance’ (or inter-changeability) of the sensory systems dealing with gravitational upright is at the basis of this interaction.
Expertise, Visual Search, and Information Pick-up in Squash
Authors: Abernethy Bruce
Published: January 2007

The visual search characteristics of expert and novice squash players were compared in two experiments. In the first experiment subjects were required to predict the forthcoming direction and force of an opponent's stroke from a film display. This film display was designed to simulate the normal display available to the defending player in squash and involved the use of variable temporal cut-offs to force the subjects to use advance cues in their prediction. Systematic differences in the information pick-up of the experts and novices were observed on the film task but these differences were achieved with only relatively minor between-group variations in visual search strategy. In the second experiment, set in the natural field setting, no expert—novice differences in either fixation distribution, order, or duration were observed on a comparable prediction task. This provided further support for the conclusion that the limiting factor in the perceptual performance of the novices is not an inappropriate search strategy but rather an inability to make full use of the information available from fixated display features. Some practical implications of these findings for the squash coach and player are considered.
Amodal Representation of Occluded Surfaces: Role of Invisible Stimuli in Apparent Motion Correspondence
Authors: Shimojo Shinsuke , Nakayama Ken
Published: January 2007

A series of demonstrations were created where the perceived depth of targets was controlled by stereoscopic disparity. A closer object (a cloud) was made to jump back and forth horizontally, partially occluding a farther object (a full moon). The more distant moon appeared stationary even though the unoccluded portion of it, a crescent, changed position. Reversal of the relative depth of the moon and cloud gave a totally different percept: the crescent appeared to flip back and forth in the front depth plane. Thus, the otherwise-robust apparent motion of the moon crescents was completely abolished in the cloud-closer case alone. This motion-blocking effect is attributed to the ‘amodal presence’ of the occluded surface continuing behind the occluding surface.

To measure the effect of this occluded ‘invisible’ surface quantitatively, a bistable apparent motion display was used (Ramachandran and Anstis 1983a): two small rectangular-shaped targets changed their positions back and forth between two frames, and the disparity of a large centrally positioned rectangle was varied. When the perceived depths supported the possibility of amodal completion behind the large rectangle, increased vertical motion of the targets was found, suggesting that the amodal presence of the targets behind the occluder had effectively changed the center position of the moving targets for purposes of motion correspondence.

Amodal contours are literally ‘invisible’, yet it is hypothesized that they have a neural representation at sufficiently early stages of visual processing to alter the correspondence solving process for apparent motion.
Motion Aftereffects from a Motionless Stimulus
Authors: Anstis Stuart
Published: January 2007

Dimming or brightening regions superimposed, slightly out of register, on static light or dark blobs, give rise to apparent motion. When these regions are replaced by apparent brightening or dimming produced by ramp aftereffects, a directional motion aftereffect is perceived. It is concluded that filters sensitive to temporal derivative signals of net brightening or dimming provide an input into the motion pathways.
Coherence Determines Speed Discrimination
Authors: Welch Leslie , Bowne Samuel F
Published: January 2007

The visual system must determine which elements in a scene to regard as parts of a single object and which to regard as different objects. We can create stimuli that are ambiguous, ie consistent with more than one interpretation, and ask in what situations the stimulus elements are interpreted as part of a single object and when they are interpreted as multiple objects. The ambiguous stimuli in this study were moving plaid patterns—the sum of two drifting gratings with different orientations. Observers may see a rigid coherent plaid object moving in one direction, or may see two gratings moving in different directions sliding over one another. When the gratings have similar contrasts they appear to cohere and only the plaid speed is perceptually available; when the gratings have different contrasts they appear to slide and only the speeds of the gratings are perceived. Coherence thus determines what speed information is passed to higher stages of motion processing. A two-stage model of plaid motion perception is presented which agrees with the model proposed by Adelson and Movshon and extends it, detailing the relationship between coherence and speed discrimination.
Visual Localization and Estimation of Extent of Target Motion during Ocular Pursuit: A Common Mechanism?
Authors: Mateeff Stefan , Hohnsbein Joachim , Ehrenstein Walter H
Published: January 2007

The ability to localize a visual target and to estimate the distance through which it moves was studied during ocular pursuit. In the first experiment observers had to localize the position of a visually tracked moving target when they heard an acoustic signal. The signal was sounded near the beginning or near the end of the motion. The distance between the perceived positions was shorter than the distance between the corresponding physical positions of the target. The ‘shortening’ became more pronounced with higher tracking velocity. In another condition the observers estimated the length of the motion path between two successive sound signals, one presented near the beginning and one near the end of the motion. The length of path travelled was underestimated, the effect being stronger with higher tracking velocity. In the second experiment this effect of velocity on the underestimation of distance was shown to exist only during ocular pursuit and not during steady fixation. The hypothesis that localization and estimation of distance during ocular pursuit share a common mechanism is discussed.
Ambiguous Fluidity and Rigidity and Diamonds that Ooze!
Authors: Meyer Glenn E , Dougherty Thomas J
Published: January 2007

If white hemicircles rotate over the edges of a black diamond, there occurs an ambiguity of rigidity and motion. As the hemicircles obscure the vertices of the diamond, the figure transforms from a diamond to a rotating, nonrigid cross made of a tar-like fluid. When the corners reappear, the stimulus again becomes a rigid, solid diamond. Visibility of the vertices implies rigidity. If white squares are rotated, fluidity is not perceived. If the diamond has sawtooth edges and the hemicircles are rotated, no fluidity is perceived. Similarly, if illusory contours suggest the amodal completion of the vertices, rigidity is maintained.
Hemifield Differences in Perceived Spatial Frequency
Authors: Edgar Graham K , Smith Andrew T
Published: January 2007

Measurements of the perceived spatial frequency of stationary sinewave gratings were made with the gratings presented at the same eccentricity in the left, right, upper, and lower visual hemifields. Ten subjects performed the task binocularly with spatial frequencies of 1, 2, and 4 cycles deg−1. Two of these subjects also performed the task monocularly at 2 cycles deg−1. In the majority of cases, the spatial frequency of stimuli presented in the left and lower visual hemifields was overestimated relative to stimuli presented in the right and upper visual hemifields. The results were similar for all spatial frequencies tested, and the direction of the asymmetry was the same whether viewing was with the left eye, right eye or binocular, suggesting that the differences in perceived spatial frequency are not retinal in origin.
Saccadic Reaction Times of Dyslexic and Age-Matched Normal Subjects
Authors: Fischer Burkhart , Weber Heike
Published: January 2007

Saccadic reaction times (SRT) were measured in a simple task: subjects had to make saccades from a central fixation point to peripheral targets, which appeared randomly 4 deg to the left or to the right. In the first test the fixation point went off before the target appeared (gap trials); in the second test it remained on the screen (overlap trials). The distribution of SRTs for trained normal adults ( N = 4), untrained normal adults ( N = 11), untrained normal children (aged 9–11 years, N = 9), untrained normal teenagers (aged 15–17 years, N = 8), dyslexic children (aged 9–11 years, N = 15), and dyslexic teenagers (aged 15–17 years, N = 5) were compared, with special emphasis on the number of express saccades, ie saccades with extremely short reaction times (100–120 ms, under the present conditions). In normal adults with the gap paradigm, the distribution of reaction times typically exhibits two or three modes (express saccades, fast regular saccades, and very few slow regular saccades), whereas in the overlap paradigm only one or two modes (few fast regular saccades and many slow regular saccades) are obtained. On average, normal children produce more express saccades than naive normal adults. Dyslexic children produce more express saccades than the normal age-matched controls. Among the dyslexic children, four different types of abnormalities in their reaction times were encountered. The group of dyslexic teenagers was characterized by a larger number of express saccades at the expense of fast regular saccades in gap trials and by fewer express saccades and fewer fast regular saccades in overlap trials when compared to the age-matched control group. It is concluded that the abnormal patterns of saccadic reaction times reflect defects in the system of visual attention and/or in its control over the oculomotor system, rather than indicating a defect in the oculomotor system itself. In this context, symptoms of dyslexia appear as a combination of attentional deficits and irregular timing of saccadic eye movements.