bluuebunny/crossref_metadata_2025 huggingface dataset:
Pattern and Orientation Effects on Afterimage Duration
Authors: Cerf-Beare Aleeza
Published: January 2007

Patterns composed of a pair of lines: vertical+horizontal, vertical+oblique, horizontal+oblique, and oblique+oblique, either centrally-aligned or edge-aligned, were shown at two positions of rotation. After a 1-s exposure to the pattern observers timed the duration of afterimages consisting of individual lines (fragmentary state) and the pattern as a whole (unitary state) for the ensuing 60 s. Summing unitary and fragmentary afterimage durations yielded the total afterimage duration for each pattern.

Three hypotheses were confirmed by the results: (i) total afterimage duration is constant for all patterns when integrated spatiotemporal luminances are equal; (ii) unitary afterimage duration is also constant; (iii) fragmentary afterimages of vertically oriented lines have longer durations than either their horizontal or oblique pair members, regardless of alignment and, with one exception, rotation. For all patterns, the durations of the unitary and the fragmentary state represent a fixed portion of the total afterimage duration. The difference between afterimage duration for differently oriented lines in patterns which include a vertical is discussed in relation to the vertical–horizontal illusion, the function and structure of cortical orientation processes, and perceptual development.
A Three-Dimensional Motion Aftereffect Produced by Prolonged Adaptation to a Rotation Simulation
Authors: Petersik J Timothy , Shepard Alexandra , Malsch Robert
Published: January 2007

After adaptation to a perspective simulation of a square plane rotating in depth, an ambiguous rotation simulation (ie one containing no perspective information) appears to rotate in the direction opposite that of adaptation. The strength of this three-dimensional motion aftereffect (MAE) is proportional to the amount of perspective available in the adaptation display and, in the dark, decays to about 75% of its initial strength within about 546 s. The nature of the testing situation and a control experiment suggest that the three-dimensional MAE is not caused by retinal adaptation of two-dimensional directionally selective mechanisms.
A Psychophysical Study of the Fuchs Phenomenon
Authors: Masin Sergio Cesare
Published: January 2007

The Fuchs phenomenon (ie the perception of transparency when the object seen through transparency lies on a homogeneous background, and does not jut out from under the transparent layer) has been studied by the numerical-rating method in two experiments, with the use of achromatic colours. The results of the first experiment show that the degree of transparency depends on the difference in colour between the object and the background. The results of the second experiment suggest that the processes producing the phenomenon are different in nature from the processes producing the kind of transparency most frequently studied in which the object juts out from under the transparent layer.
Independent Processing of Visual form and Motion
Authors: Krumhansl Carol L
Published: January 2007

Rotating or stationary targets were presented simultaneously with a random-dot mask which was itself either rotating or stationary. Observers were required to judge both the form of the target and its motion; these target attributes were manipulated orthogonally in the experiment. The results support the hypothesis that under these conditions figural information is encoded independently from motion information. On a trial-by-trial basis within conditions of target and mask motion combinations, performance in the two tasks was independent. Across conditions, different effects were observed in the two dependent measures. Form judgments were generally more accurate for rotating than for stationary targets, particularly when the mask was stationary. Motion judgments showed frequent intrusions from the motion of the mask, so that most errors occurred when target and mask were dissimilar in terms of their motion. The results show differential interference of the random-dot mask on the encoding of the two independent stimulus attributes, and support the possibility of separate processing of figural and motion information.
Acuity of Sound Localisation: A Topography of Auditory Space. I. Normal Hearing Conditions
Authors: Oldfield Simon R , Parker Simon P A
Published: January 2007

Eight subjects were required to localise a sound source (white noise through a speaker) which varied in position on both sides of the head over a range of elevations (-40° to +40°) and azimuths (0° to 180°) at 10° intervals. The perceived position of the source was indicated by pointing a special gun. Depression of the trigger activated a photographic system which recorded two views of the subject, the sound source, and the gun. The absolute and algebraic, azimuth and elevation errors were measured for all subjects at each position of the source. The variability of azimuth and elevation error was also computed. In a second experiment, four of the same subjects performed the same task but in this case visually located the sources. This experiment provided an estimate of inherent motor error in the pointing task. No differences in localisation acuity between sides were found, but there were significant differences between front and back regions. Azimuth and elevation error were well matched and low in the front. However, azimuth error increased in the regions behind the head, particularly for azimuth positions 120° to 160°. Larger increases were found for positions in the upper elevations of this region. Elevation error also increased in the upper elevations behind the head. A comparison of the auditory and visual data indicates that this pattern of error is not due to motor factors. The results are discussed in relation to the structural characteristics of the pinnae and modifications that they impose on incoming sound energy.
Detection versus Discrimination of Visual Orientation
Authors: Sagi Dov , Julesz Bela
Published: January 2007

The role of focused attention in vision is examined. Recent theories of attention hypothesize that serial search by focal attention is required for discrimination between different combinations of features. Experiments are reported which show that the mixture of a few (less than five) horizontal and vertical line segments embedded in an aggregate of diagonal line segments can be rapidly counted (also called ‘subitizing’) by a parallel (preattentive) process, while the discrimination between horizontal and vertical orientation requires serial search by shifting focal attention to each line segment. Thus detecting and counting targets that differ in orientation can be done in parallel by a preattentive process, whereas knowing ‘what’ the orientation of a target is (horizontal or vertical, ie of a single conspicuous feature) requires a serial search by focal attention.
The Effects of Exposure to Red and Blue Light on Physiological Indices and Time Estimation
Authors: Caldwell John A , Jones Gary E
Published: January 2007

The effects of exposure to red, white, and blue lights on time estimation and physiological indices were examined. Sixty subjects were exposed to a total of four presentation series of red, white, and blue lights. There were two phases of the experiment: a verbal estimation phase in which subjects were required to count out loud the length of each color while measures of eyeblinks, skin conductance, pulse volume, heart rate, and EEG activity were obtained; and a production phase in which subjects were required to produce several intervals while measures of EEG were obtained. The data on each dependent measure were subjected to three-way repeated-measures ANOVAS. EEG data were digitized and analyzed with power spectral, peak frequency, percentage of alpha activity, and discriminant analyses. Results indicate that color did not exert consistent significant effects on any of the dependent measures and raise serious questions about the assumption that ‘warm’ colors are more arousing than ‘cool’ colors.
The Role of Object-Hypotheses in the Organization of Fragmented Figures
Authors: Reynolds Robert I
Published: January 2007

The effect of an object-hypothesis on the organization of fragmented figures was investigated by varying instructions given prior to stimulus presentation. One group was uninformed as to the possibility of seeing a figure; a second group was instructed that it is possible to see a meaningful object; a third group was further instructed as to which class of object was presented. It was found that, in order to achieve organization of fragmented figures, the observer must have knowledge that a meaningful object may be integrated from the fragments. Knowledge of the class of object, while increasing the likelihood of recognition, does not significantly decrease search time.
It's All Done with Mirrors: Proof of Non-Existence
Authors: Kennedy John M
Published: January 2007

Mirrors can show us to be absent (with minimal cognitive damage) and also can show imaginary lines to be unreal (again with little or no effect on the adjoining percept). The processes that create the subjective lines are immune to the optic information that the lines do not exist.
Texture Discrimination Does Not Occur at the Cyclopean Retina
Authors: Nothdurft H C
Published: January 2007

The ability to segregate texture patterns at the cyclopean retina was tested with random-dot stereograms. When fused, patterns displayed arrays of texture elements which varied either in their form or in apparent depth. If elements of different form appeared at similar disparity in the random-dot stereograms, they did not provide the visual impression of distinct texture areas, although individually they could be easily discriminated. When texture elements differed in apparent depth rather than in form, segregation of different areas was readily achieved. These results restrict the possible site in the visual system for texture discrimination.
Apparent Reversals in Trapezia: Confirmation of the ‘Tan Apex Ratio’ Heuristic
Authors: Mitchell Rex , Power Roderick P
Published: January 2007

A new model for predicting the frequencies of apparent reversals in rotating trapezia, proposed by the authors in 1983, is validated and extended in two studies. Experiment 1 showed that the model retained its predictive efficiency over an increased range of shapes and viewing distances, and with trapezia made of sheet metal and not, as previously, of wire. Experiment 2 was designed to investigate an unexpected effect, in which the specificity of prediction was found to decrease as the corners of the stimulus objects were slightly rounded.
A Color-Contingent Prism Displacement Aftereffect
Authors: Donderi Don C , Jolicoeur Pierre , Berg Ian , Grimes Robert
Published: January 2007

Observers were trained to point with feedback to red and blue dots whose images had been laterally displaced in opposite directions by a reversible prism. On pretraining and posttraining trials the red and blue dots were aligned vertically in the absence of visual orientation cues. The alignment was modified by the pointing training on the posttraining trials. The colors were aligned in the direction of their prior prismatic displacement. One control experiment showed that the alignment aftereffect, requires feedback during the pointing task. Another experiment in which observers pointed to the red and blue dots with opposite arms showed that pointing to both dots with the same arm was necessary to produce the alignment aftereffect. Changes in the perceived position of objects in the visual field occur when changes in perceived limb position cannot compensate for a sensorimotor conflict. Eye torsion or fixation displacements are proposed as alternative mechanisms mediating the aftereffect.
Figure-Background Perception in Right and Left Hemispheres of Human Commissurotomy Subjects
Authors: Cronin-Golomb Alice
Published: January 2007

The right and left hemispheres of four complete commissurotomy subjects were tested for the ability to recognize and integrate figure and background elements of composite visual stimuli. In the first experiment the subjects were required to identify from a four-choice array in free vision the stimulus card that matched the briefly lateralized sample stimulus. For all subjects the left hemisphere was proficient at identifying the figure, but performed at near-chance level in recognizing the textured background. In contrast, the right hemisphere was equally adept at identifying figures and backgrounds. Both hemispheres could easily identify the isolated figure or background from a choice array, demonstrating that the observed hemisphere effects were due to figure–background interactions rather than the result of any difficulty in processing specific elements of the composite stimulus. The second experiment involved the determination of the size and position of a dot that appeared against various plain and textured backgrounds. The right hemisphere of two subjects, but not the left, performed with greater accuracy when the background consisted of a ‘natural’ texture gradient rather than a plain white backing. Similar though less consistent results were obtained when an inverted gradient or an evenly spaced grid was used as the background. For each condition, right-hemisphere performance resembled that of normal control subjects. In contrast, the left hemisphere provided a pattern of results dissimilar to that of control subjects for the various figure–background tasks described. It appeared to be generally insensitive to background effects, except when the information provided by the background was highly unusual, as from an inverted texture gradient. The results suggest a preeminent role for the right hemisphere in (i) the recognition of background components of a whole-field stimulus, (ii) sensitivity to the influence of the background on the perception of an object, and (iii) the ability to use natural perspective cues to assist in the accurate perception of an object.
The Role of Spatial-Frequency Channels in the Perception of Local and Global Structure
Authors: Shulman Gordon L , Sullivan Marc A , Gish Ken , Sakoda William J
Published: January 2007

Adaptation and reaction-time techniques were used to examine the role of different spatial-frequency channels in the perception of local and global structure. Subjects were shown figures consisting of a large C composed of smaller Cs and asked to identify the orientation of either the global C or its local elements. Prior to performing the task subjects were adapted to different spatial frequencies and the effect on subsequent performance was assessed. Two main results were found. First, the adapting frequency that most affected the global task was often lower than that most affecting the local task, suggesting that high and low frequencies independently code the structure of an image. Second, reaction time to global figures was often faster than to local figures at all levels of detectability, again suggesting a role of low-frequency channels in global processing.
Spatial Organization of the Diplesthetic and Nondiplesthetic Areas of the Fingers
Authors: Benedetti Fabrizio
Published: January 2007

Cutaneous points on different fingers were brought into contact with each other to ascertain whether one stimulus was perceived to be single or double. The perceptual responses were mapped on the five fingertip pads. The results show that there is an extensive cutaneous area on each fingertip pad which elicits one-stimulus perceptions when a single stimulus is applied between each finger and the thumb. This area decreases when the stimulus is applied to adjacent fingers (2–3, 3–4, 4–5), and even more so when it is applied to nonadjacent fingers (2–4, 2–5, 3–5). In fact, in adjacent and nonadjacent fingers the cutaneous surface eliciting a doubling of the single stimulus (diplesthesia) is very extensive. The spatial arrangement of the cutaneous areas eliciting single perceptions appears to be invariant in the proximo-distal plane. Instead, the shift from one kind of perception to another occurs in the medio-lateral plane. It is suggested that this perceptual organization could reflect a neural organization.
Visual Object Recognition in Patients with Right-Hemisphere Lesions: Axes or Features?
Authors: Warrington Elizabeth K , James Merle
Published: January 2007

An investigation is reported of the ability of normal subjects and patients with right-hemisphere lesions to identify 3-D shadow images of common objects from different viewpoints. Object recognition thresholds were measured in terms of angle of rotation (through the horizontal or vertical axis) required for correct identification. Effects of axial rotation were very variable and no evidence was found of a typical recognition threshold function relating angle of view to object identification. Although the right-hemisphere-lesion group was consistently and significantly worse than the control group, no qualitative differences between the groups were observed. The findings are discussed in relation to Marr's theory that the geometry of a 3-D shape is derived from axial information, and it is argued that the data reported are more consistent with a distinctive-features model of object recognition.
Flicker Masking and Developmental Dyslexia
Authors: Smith Andrew T , Early Frances , Grogan Sarah C
Published: January 2007

Recent studies have provided evidence that dyslexic children tend to show longer visual persistence than control children when presented with low-spatial-frequency grating stimuli. The possibility that this phenomenon might reflect an impairment of inhibitory Y-cell activity in the visual system of dyslexics has been investigated. A flicker masking technique was used to mask Y-cell activity selectively in a group of dyslexic boys and a group of age-matched controls. There were no overall differences in reaction times to the offsets of grating patterns of various spatial frequencies between the groups, and no differences between subgroups defined by age, degree of reading impairment, or any other criterion. The results show no evidence of abnormal Y-cell function in developmental dyslexia.
Stereokinesis with Moving Visual Phantoms
Authors: Bressan Paola , Vallortigara Giorgio
Published: January 2007

When a flat pattern composed of a solid ellipse with two symmetrical semirings (corresponding to the visible parts of a contour ellipse whose major axis is perpendicular to that of the solid ellipse) is slowly rotated in the frontoparallel plane, a compelling three-dimensional impression occurs. Subjects report seeing an egg-shaped object that is inserted into a circular ring: the two objects move solidly into three-dimensional space and a moving visual phantom is generated so that the ring appears completed by an illusory curved bar in the region closest to the observer during rotation. A number of variations of this illusion are presented. It is shown that stereokinetic phantoms (i) maintain the shape of the inducing elements; (ii) appear only after the stereokinetic transformation has taken place; and (iii) depend on the organization of the three-dimensional percept as a whole. Relations between stereokinetic phantoms and other completion phenomena are presented and discussed.
Attention—Dependent Visual Capture in Double Vision
Authors: Shimojo Shinsuke
Published: January 2007

When the visual image of a body part, such as a finger, is doubled by a prism, the ‘felt’ position of that body part is captured by one of its visual images. Moving eye fixation from one to the other visual image is accompanied by a quick shift of the felt position. When focal attention is dissociated from foveation, the former determines visual capture. These new observations underline an active role of focal attention in intersensory integration and sensory—motor coordination of body parts.
Visual Imagery Selectively Reduces Vernier Acuity
Authors: Craver-Lemley Catherine , Reeves Adam
Published: January 2007

Mental imagery interferes with perception. This, an example of the ‘Perky effect’, was studied for vernier acuity. Mean accuracy for reporting the offset of vertical line targets declined from 80% to 65% when subjects were requested to imagine vertical lines near fixation. Images of horizontal lines or of a grey mist in the fixation region lowered accuracy to a similar extent. However, accuracy was barely affected when the image was requested 1.5 deg or more from the target. The Perky effect remained strong for at least 4 s after an instruction to ‘clear’ the image away. The results were not due to imagery-induced changes in fixation, pupil diameter, or accommodation, or (at least primarily) to central attentional or decisional factors. Rather, imagery produces a local, pattern-insensitive, and relatively long-lasting reduction in visual sensitivity. The sensitivity loss may be mimicked by a 0.24 log unit reduction in target energy.
Detection of Moving Local Density Differences in Dynamic Random Patterns by Human Observers
Authors: Casco Clara , Morgan Michael
Published: January 2007

The way in which movement enhances target visibility has been investigated by measuring the detectability of the direction of motion of a dot pattern added to a background of dynamic visual noise. When the positions of all the dots were changed randomly from frame to frame, so that there was no dot configuration to define the target area (experiments 1 and 2), the threshold density difference necessary was for direction of motion detection less than 3 dots/frame (between 20% and 50% density difference). The spatial displacement (S) at which optimal detection occurs increased when a target elongated in the direction of motion was used. If S was either larger or smaller than its optimal value, thresholds rose progressively. The rise in threshold when S was smaller than 0.25 deg (the width of the target area) decreased when the target dots had a fixed spatial arrangement (experiment 3). It is suggested that in both fixed and random target configurations there is a grouping of dots with similar trajectories via a global directionally-selective process. The strength of the overall motion signal is greater in the fixed-dot configuration because each target dot has associated with it a vector precisely aligned in the direction of the target motion.
Signal Processing Strategies for Electrostimulated Ear Prostheses Based on Simulated Nerve Response
Authors: Motz Hans , Rattay Frank
Published: January 2007

Improvements to the coding strategy of prostheses for the profoundly deaf which can be implemented by the speech processors of these devices are suggested. Difficulties with vowel recognition are diagnosed as being due to nerve properties. These are studied with the aid of a model in order to find ways of overcoming the difficulties.
Perceptual Alternations in Stereokinesis
Authors: Vallortigara Giorgio , Bressan Paola , Bertamini Marco
Published: January 2007

When a flat ellipse is slowly rotated in the frontoparallel plane, two different 3-D percepts can be obtained: (i) a rigid circular disc tilting back and forth in 3-D space, and (ii) an elongated egg, slanted into 3-D space, whose end parts seem to be located at different distances from the observer and describe a circular trajectory with respect to the frontal plane. Under prolonged observation, the two 3-D percepts alternate in time, separated by brief intervals in which either the rotation of a rigid flat ellipse in the frontal plane or an amoeba-like distortion of a 2-D shape can be perceived. An experiment is reported in which the sequence of perceptual alternations was investigated. Results show that the 3-D disc is mostly preceded by impressions of elastic amoeba-like deformations, whereas the 3-D egg is mostly preceded by the percept of a rotating flat ellipse. Direct transitions from egg to disc are not as frequent as transitions from disc to egg. Results are discussed in relation to Braunstein and Andersen's hypothesis that phenomena of this sort might result from the stimulation of automatic mechanisms for perceiving size change (changing—size neural channels).
Looking at Faces: First-Order and Second-Order Features as Determinants of Facial Appearance
Authors: Rhodes Gillian
Published: January 2007

The encoding and relative importance of first-order (discrete) and second-order (configural) features in mental representations of unfamiliar faces have been investigated. Nonmetric multidimensional scaling (KYST) was carried out on similarity judgments of forty-one photographs of faces (homogeneous with respect to sex, race, facial expression, and, to a lesser extent, age). A large set of ratings, measurements, and ratios of measurements of the faces was regressed against the three-dimensional KYST solution in order to determine the first-order and second-order features used to judge similarity. Parameters characterizing both first-order and second-order features emerged as important determinants of facial similarity. First-order feature parameters characterizing the appearance of the eyes, eyebrows, and mouth, and second-order feature parameters characterizing the position of the eyes, spatial relations between the internal features, and chin shape correlated with the dimensions of the KYST solution. There was little difference in the extent to which first-order and second-order features were encoded. Two higher-level parameters, age and weight, were also used to judge similarity. The implications of these results for mental representations of faces are discussed.
The Psychophysics of Retrospective and Prospective Timing
Authors: Brown Scott W , Stubbs D Alan
Published: January 2007

In two experiments, different groups of subjects heard four musical selections and then estimated the duration of each selection. Some groups made retrospective time estimates while others made prospective estimates. In both experiments, analyses of the psychophysical relation between perceived and actual duration showed that the slopes of straight-line fits were flatter and accounted for a smaller proportion of the variance under retrospective as compared with prospective conditions. In addition, in experiment 1, retrospective subjects were less accurate in rank ordering the selections from longest to shortest. There was also a serial-order effect, with selections estimated longer when they occurred early in the sequence. In experiment 2 the slopes decreased as the selections in a series became longer. Both retrospective and prospective estimates also exhibited a context effect, in that estimates of a given selection were influenced by the relative durations of the other three selections in the series. The results on inaccurate retrospective judgments raise questions about prior research on stimulus factors and retrospective timing. However, similarities under retrospective and prospective conditions suggest that timing under these conditions, although different in some respects, reflects a similar process.
The Effect of Feature Displacement on the Perception of Well-Known Faces
Authors: Hosie Judith A , Ellis Hadyn D , Haig Nigel D
Published: January 2007

The effect of feature displacement within two well-known faces (Terry Wogan and Cyril Smith) was examined. Image processing equipment was used to produce stimuli in which the features of an original facial image were displaced to form a number of modified images. This technique was first reported by Haig, in a recognition study in which the effect of feature displacement within unfamiliar faces was investigated. In the present experiment a perceptual judgement task was carried out in which subjects were presented with a number of modified faces and asked to judge how dissimilar these were with respect to an original image. A multidimensional scaling analysis of the comparative judgements of the subjects revealed a two-dimensional solution involving displacement of the eyes and mouth. A clear division between up/down and inward/outward displacement within these features (particularly the eyes) was observed. A similar pattern of results was found for both well-known faces. This result indicates that subjects were responding to changes in the facial configuration produced by the different types of feature displacement (horizontal or vertical), as opposed to movement of the features per se. Finally, the results also indicate that the displacement of inner features (mouth, eyes, nose) was more noticeable than displacement of the outer facial features (eg hairline).
Feature Saliency in Judging the Sex and Familiarity of Faces
Authors: Roberts Tony , Bruce Vicki
Published: January 2007

Two experiments are reported on the effect of feature masking on judgements of the sex and familiarity of faces. In experiment 1 the effect of masking the eyes, nose, or mouth of famous and nonfamous, male and female faces on response times in two tasks was investigated. In the first, recognition, task only masking of the eyes had a significant effect on response times. In the second, sex-judgement, task masking of the nose gave rise to a significant and large increase in response times. In experiment 2 it was found that when facial features were presented in isolation in a sex-judgement task, responses to noses were at chance level, unlike those for eyes or mouths. It appears that visual information available from the nose in isolation from the rest of the face is not sufficient for sex judgement, yet masking of the nose may disrupt the extraction of information about the overall topography of the face, information that may be more useful for sex judgement than for identification of a face.
How Contrast Affects Stereoacuity
Authors: Halpern D Lynn , Blake Randolph R
Published: January 2007

Stereoacuity and its dependence on contrast were measured at four spatial frequencies separated by 1 octave steps. Using a method of adjustment, observers adjusted the retinal disparity of an aperiodic narrow-band stimulus until it appeared in the depth plane defined by two flanking reference lines. Variations in contrast affected stereoacuity (the standard deviation of ten depth settings), with better performance observed at higher contrasts. Data were fit with straight lines (on a log–log plot), indicating a power-law dependence on contrast; the slope was steeper at lower spatial frequencies. These findings are consistent with the idea that disparity is computed from the responses of size-tuned mechanisms characterized by nonlinear contrast transfer functions. In a second experiment, the effects of interocular differences in contrast on stereoacuity were studied for two conditions. In the first condition, one eye always viewed a high-contrast target while the other eye viewed targets of successively lower contrast; in the second condition, one eye always saw a target of near-threshold contrast while the other eye saw targets of successively higher contrast. When the fixed contrast was high, stereoacuity deteriorated steadily as the interocular difference in contrast increased; the loss of stereoacuity was greatest at the lowest spatial frequency. When the fixed contrast was low, however, small increases in the contrast to one eye had no deleterious effect on stereoacuity. Once interocular contrast settings exceeded a certain difference, stereoscopic acuity began to deteriorate at lower spatial frequencies. These results address the issue of the stage of visual processing at which contrast exerts its influence on stereopsis.
Temporal Properties of Apparent Motion in Subjective Figures
Authors: Mather George
Published: January 2007

In ‘Kanizsa’ figures, vivid subjective shapes are seen in the absence of explicit contours to define them. When two or more such figures are presented sequentially, so that the subjective shape occupies different positions, good apparent motion of the shape is usually reported. This motion percept must be mediated by a high-level process, in which form extraction precedes motion detection. Some spatial and temporal properties of this motion process are investigated. A major finding is that motion is only perceived when the time interval between successive frames falls below about 500 ms, and the duration of each frame exceeds about 80 ms.
Size Constancy in Children: A New Interpretation
Authors: Shallo Josephine , Rock Irvin
Published: January 2007

Existing evidence indicates that there are differences between children and adults in size constancy when observation distances are large. Findings are reported which suggest that this phenomenon is based on a difference in the accessing of proximal stimulus information, which, in the case of size, refers to visual angle subtended. Age differences were found when a traditional size constancy task was used, but these differences disappeared when all the comparison objects subtended the same visual angle. Since this finding demonstrates that young children can make accurate size matches, it is suggested that the underconstancy previously reported is not necessarily the result of childrens' inability to use fully certain cues to distance. Rather, the findings suggest that children access proximal stimulus information more spontaneously than do adults.
Stereoscopic Depth: Its Relation to Image Segmentation, Grouping, and the Recognition of Occluded Objects
Authors: Nakayama Ken , Shimojo Shinsuke , Silverman Gerald H
Published: January 2007

Image regions corresponding to partially hidden objects are enclosed by two types of bounding contour: those inherent to the object itself (intrinsic) and those defined by occlusion (extrinsic). Intrinsic contours provide useful information regarding object shape, whereas extrinsic contours vary arbitrarily depending on accidental spatial relationships in scenes. Because extrinsic contours can only degrade the process of surface description and object recognition, it is argued that they must be removed prior to a stage of template matching. This implies that the two types of contour must be distinguished relatively early in visual processing and we hypothesize that the encoding of depth is critical for this task. The common border is attached to and regarded as intrinsic to the closer region, and detached from and regarded as extrinsic to the farther region. We also suggest that intrinsic borders aid in the segmentation of image regions and thus prevent grouping, whereas extrinsic borders provide a linkage to other extrinsic borders and facilitate grouping. Support for these views is found in a series of demonstrations, and also in an experiment where the expected superiority of recognition was found when partially sampled faces were seen in a back rather than a front stereoscopic depth plane.
Necessary Considerations for a Theory of Form Perception: A Theoretical and Empirical Reply to Boselie and Leeuwenberg (1986)
Authors: Peterson Mary A , Hochberg Julian
Published: January 2007

Boselie and Leeuwenberg (1986) recently defended their version of the minimum principle, called structural information theory or SIT, against a varied set of criticisms. Two of the most notable of these criticisms are (i) that perceptual organization can proceed as a piecemeal, rather than as a global, process (as demonstrated by partially-biased Necker cubes and ‘impossible’ figures), and (ii) that perceptual organization is influenced by subjective variables as well as by stimulus variables (Peterson and Hochberg 1983). The second criticism was acknowledged by Boselie and Leeuwenberg but not addressed. The first criticism was addressed by the introduction of two new variables into SIT in order to argue that the perceived organization of partially-biased Necker cubes and impossible figures can be predicted by a global coding scheme, thereby supporting rather than refuting global minimum principles. It is argued here that the criticisms cannot be dismissed by this rebuttal, which is focused narrowly on single examples rather than on the general principles embodied by the demonstrations. The implications of piecemeal perception and subjective mediation are spelled out, and both old and new data showing that the applicability of global minimum principles must be reexamined, not merely defended, are discussed. Finally, the argument for a richer, more interacting, theory of form perception is presented.
Globally Perceived Directional Flow in Static Images
Authors: Farell Bart , Julesz Bela
Published: January 2007

Visual sensitivity to spatial direction has classically been associated with motion perception. Yet humans are adept at deriving directional information in the absence of motion, as when they read maps, or follow arrows or animal tracks. Experiments are reported on the perception of parallel arrow-like forms in which a specific visual sensitivity to static direction is demonstrated. Global processing is operationally defined in terms of the relative discriminability of sets and subsets of stimulus elements; a set of parallel elements and a set in which one element is antiparallel to the rest are shown to be processed globally. The result of this global processing is a static analog of unidirectional optic flow. Global spatial direction differs fundamentally from other perceptions derived from static image processing. It involves long-range interactions in texture arrays, it does not carry information about stimulus location, and it is not reducible to the perception of component stimulus elements. Its likely function is in the construction of the layout of visual space.
Rotating Trapezia Which Appear Luminous and Transparent during Reversals
Authors: Cowie Roddy
Published: January 2007

If a rotating trapezium is lit by a visible source at one side, it sometimes reflects light to the observer and sometimes appears dark. This provides information about its orientation which is relevant to the suppression of apparent reversals. Marked suppression does occur if the light is between the observer and the object, but in other cases novel phenomena arise. The onset of light may precipitate corrections, ie discontinuous shifts from an illusory percept to a veridical one. At certain stages the object may also appear to be transparent and luminous, particularly if a bar has been passed through it: the bar then appears to be visible through the object. The effects illustrate the limited use vision makes of seemingly excellent sources of information, but they also indicate that the problem may lie in misplaced sophistication rather than crudity.
How Serial is Serial Processing in Vision?
Authors: Zohary Ehud , Hochstein Shaul
Published: January 2007

Visual search for an element defined by the conjunction of its colour and orientation has previously been shown to be a serial processing task since reaction times increase linearly with the number of distractor elements used in the display. Evidence is presented that there are parallel processing constituents to this serial search. Processing time depended on the ratio of the number of the two distractor types used, suggesting that only one type was scanned. Which type was scanned also depended on the distractor ratio, indicating that this decision was made after stimulus presentation and was based on a parallel figure—ground separation of the stimulus elements. Furthermore, in accordance with this serial scanning model, there was an increase in processing speed (elements scanned per second) with increase in number of elements to be scanned. This increased efficiency suggests that clumps of elements were processed synchronously. Under the stimulation conditions used, clumps contained six to sixteen elements and each clump was processed in 50–150 ms.
Misaligned Maps Lead to Predictable Errors
Authors: Rossano Matt J , Warren David H
Published: January 2007

Three experiments were conducted to investigate the ability of subjects to make judgments of direction when using misaligned maps. Two hypotheses were proposed: (i) errors would fall into two lawful categories—mirror-image errors and alignment errors; (ii) the effect of map orientation would generalize to a different mode of responding than has been used in previous studies. Support for both hypotheses was obtained. The results are discussed in terms of the mental processes used to align maps to spaces, and the task demands required by different response modes.
Effects of Phosphor Persistence on Perception and the Control of Eye Movements
Authors: Neary Catherine , Wilkins Arnold J
Published: January 2007

When a rapid eye movement (saccade) is made across material displayed on cathode ray tube monitors with short-persistence phosphors, various perceptual phenomena occur. The phenomena do not occur when the monitor has a long-persistence phosphor. These phenomena were observed for certain spatial arrays, their possible physiological basis noted, and their effect on the control of eye movements examined. When the display consisted simply of two dots, and a saccade was made from one to the other, a transient ghost image was seen just beyond the destination target. When the display consisted of vertical lines, tilting and displacement of the lines occurred. The phenomena were more intrusive for the latter display and there was a significant increase in the number of corrective saccades. These results are interpreted in terms of the effects of fluctuating illumination (and hence phosphor persistence) on saccadic suppression.
Manual Asymmetry in Weight Discrimination: Hand or Spatial-Field Advantage?
Authors: Brodie Eric E
Published: January 2007

Sixty subjects who were either left-handed or right-handed performed one-handed weight discrimination using their left and right hands in the left and right spatial fields. Differential thresholds, for the left and right hands of both left-handed and right-handed subjects, were found to be lower in the spatial field contralateral to the ear which proved superior in a dichotic listening test. It is concluded that manual asymmetry for weight discrimination results primarily from the mapping of sensorimotor events in the spatial fields onto contralateral cerebral cortex, with an advantage in the spatial field contralateral to the nonlanguage cerebral hemisphere.
Integration of Stereo and Texture Cues in the Formation of Discontinuities during Three-Dimensional Surface Interpolation
Authors: Buckley David , Frisby John P , Mayhew John E W
Published: January 2007

A series of stereograms are presented which demonstrate that texture boundaries can strongly influence the perception of discontinuities between neighbouring three-dimensional (3-D) surfaces portrayed by means of stereo cues. In these demonstration figures, no stereo information is available in the immediate vicinity of the boundary between the two 3-D stereo surfaces because all texture in that region is removed in one eye's view. On the other hand, various forms of texture boundary information are provided in the resulting monocular region. This stimulus paradigm is used to explore the question: what influence does texture boundary information have on the nature of the perceived 3-D surface that is interpolated between two stimulus regions which carry stereo cues? It is shown that if a clear-cut texture boundary is present in the monocular region then this is used by the human visual system to fix the perceived location of 3-D crease and step surface discontinuities between the stereo regions. Collett (1985) explored this issue with a similar methodology and reported weak and unreliable assistance from monocular texture boundaries in helping shape 3-D stereo surface discontinuities. The strong and robust phenomena demonstrated here seem to rely on two main differences between the present stimuli and those of Collett. In the present stimuli, figurally continuous textures containing strong texture boundaries are used, together with a technique for minimising the complications, including binocular rivalry, that arise from the borders of the stimulus regions present in only one half of each stereogram.
The Importance of Velocity Gradients in the Perception of Three-Dimensional Rigidity
Authors: De Bruyn Bart , Orban Guy A
Published: January 2007

Sequential presentation of a number of random-dot patterns which when superimposed yield an expanding flow field leads to the perception of a coherent motion towards the observer. The motion vectors in this type of flow field all radiate from the origin. This percept of a global coherent expanding flow results only when the local speeds (magnitude of the local motion vectors) are zero at the centre and increase linearly towards the periphery. If all the dots radiate outwards but have the same speed, a clear percept of three-dimensional nonrigidity arises.
Measurement of Visual Aftereffects and Inferences about Binocular Mechanisms in Human Vision
Authors: Wilcox Laurie M , Timney Brian , St John Robert
Published: January 2007

There is conflicting evidence concerning the characteristics of binocular channels in the human visual system with respect to the existence of a ‘pure’ binocular channel that responds only to simultaneous stimulation of both eyes. Four experiments were conducted to resolve these discrepancies and to evaluate the evidence for the existence of such an exclusive binocular channel. In the first three studies, tilt aftereffects were measured after monocular adaptation. The relative sizes of the direct, interocularly transferred, and binocular aftereffects were not influenced by the configuration of the adapting pattern (experiment 1), or by the eye used for adaptation (experiment 2). There were also consistent interobserver differences in the relative sizes of the aftereffect seen after monocular adaptation (experiment 3). Taken together, these data raise questions about the appropriateness of a monocular adaptation paradigm for evaluating the presence of a pure binocular channel in observers with normal binocular vision. In experiment 4, in which the paradigm of alternating monocular adaptation was used, data were obtained that are consistent with the presence of a pure binocular channel.
The Relationship between Visual Persistence and Event Perception in Bistable Motion Display
Authors: Casco Clara
Published: January 2007

observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable apparent motion.
Apparent Brightness Enhancement in the Kanizsa Square with and without Illusory Contour Formation
Authors: Dresp Birgitta , Lorenceau Jean , Bonnet Claude
Published: January 2007

The perceived strength of darkness enhancement in the centre of surfaces surrounded or not surrounded by illusory contours was investigated as a function of proximity of the constituent elements of the display and their angular size. Magnitude estimation was used to measure the perception of the darkness phenomenon in white-on-grey stimuli. Darkness enhancement was perceived in both types of the stimuli used, but more strongly in the presence of illusory contours. In both cases, perceived darkness enhancement increased with increasing proximity of the constituent parts of the display and with their angular size. These results suggest that the occurrence of darkness (or brightness) enhancement phenomena in the centre of the displays is not directly related to illusory contour formation.