bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive Filtering in Spatial Vision: Evidence from Feature Marking in Plaids
Authors: Georgeson Mark A , Meese Tim S
Published: November 2005

Much evidence shows that early vision employs an array of spatial filters tuned for different spatial frequencies and orientations. We suggest that for moderately low spatial frequencies these preliminary filters are not treated independently, but are used to perform grouping and segmentation in the patchwise Fourier domain. For example, consider a stationary plaid made from two superimposed sinusoidal gratings of the same contrast and spatial frequency oriented ±45° from vertical. Most of the energy in a wavelet-like (eg simple-cell) transform of this stimulus is in the oblique orientations, but typically it looks like a compound structure containing blurred vertical and horizontal edges. This checkerboard structure corresponds with the locations of zero crossings in the output of an isotropic (circular) filter, synthesised from the linear sum of a set of oriented basis-filters (Georgeson, 1992 Proceedings of the Royal Society of London, Series B249 235–245). However, the addition of a third harmonic in square-wave phase causes almost complete perceptual segmentation of the plaid into two overlapping oblique gratings. Here we confirm this result psychophysically using a feature-marking technique, and argue that this perceptual segmentation cannot be understood in terms of the zero crossings marked in the output of any static linear filter that is sensitive to all of the plaid's components. If it is assumed that zero crossings or similar are an appropriate feature-primitive in human vision, our results require a flexible process that combines and segments early basis-filters according to prevailing image conditions. Thus, we suggest that combination and segmentation of spatial filters in the patchwise Fourier domain underpins the perceptual segmentation observed in our experiments. Under this kind of image-processing scheme, registration across spatial scales occurs at the level of spatial filters, before features are extracted. This contrasts with many previous schemes where feature correspondence is required between spatial edge-maps at different spatial scales.
Perceived Shape Regularity Does Not Depend on Regularities along the Contour
Authors: Hulleman Johan , Boselie Frans
Published: November 2005

In four experiments we investigated whether human observers are able to use certain regularities in polygons when they have to indicate which polygon they perceive as the more regular in a paired comparison task. From our results we conclude that regularities that are restricted to the contour do not play a role in judgments of regularity. For instance, equilateral polygons are not considered to be more regular than entirely random polygons. Only bilaterally symmetric polygons are consistently judged as regular. However, we show that this is caused by regularities across the polygon. These results are at odds with approaches that assume that regularities along the contour play an important part in visual perception.
Development of Illusory-Contour Perception in Infants
Authors: Curran William , Braddick Oliver J , Atkinson Janette , Wattam-Bell John , Andrew Rachel
Published: November 2005

We investigated whether infants from 8–22 weeks of age were sensitive to the illusory contour created by aligned line terminators. Previous reports of illusory-contour detection in infants under 4 months old could be due to infants' preference for the presence of terminators rather than their configuration. We generated preferential-looking stimuli containing sinusoidal lines whose oscillating, abutting terminators give a strong illusory contour in adult perception. Our experiments demonstrated a preference in infants 8 weeks old and above for an oscillating illusory contour compared with a stimulus containing equal terminator density and movement. Control experiments excluded local line density, or attention to alignment in general, as the basis for this result. In the youngest age group (8–10 weeks) stimulus velocity appears to be critical in determining the visibility of illusory contours, which is consistent with other data on motion processing at this age. We conclude that, by 2 months of age, the infant's visual system contains the nonlinear mechanisms necessary to extract an illusory contour from aligned terminators.
Influence of Body Roll on Visually Induced Sensations of Self-Tilt and Rotation
Authors: Groen Eric L , Howard Ian P , Cheung Bob S K
Published: November 2005

Illusory self-tilt and illusory self-motion (vection) produced by rotation of a 360° visual scene about the subject's roll axis was measured as a function of the presence or absence of actual rotation of the subject during acceleration of the visual scene. Rotation of the subject to a tilt of 15° was at two levels of acceleration (onset) and with or without a delay between initial rotation and subsequent return (washout) to the vertical position. In one set of conditions, visual motion and subject motion were in opposite directions (concordant) and in another set they were in the same direction (discordant). In two control conditions, the subject was rotated while the visual scene remained stationary. For concordant motion the main effect of body rotation was to reduce the time taken by the subject to indicate self-tilt as compared with the response time to visual motion alone. The magnitude of estimated self-tilt was increased by actual body tilt as could be expected from addition of the perceived actual body tilt and the illusory body tilt induced by visual rotation. This effect of augmented body tilt did not persist after the body was returned to the vertical. The magnitude of vection was not markedly influenced by body rotation and washout. For discordant motion of body and the visual scene, subjects were confused and their responses were very variable, suggesting a nonlinear visual-vestibular interaction.
Visual Perception in ‘Low Vision’
Authors: Hyvärinen Lea
Published: November 2005

‘Low vision’ has an international classification as an impairment of vision that is defined by loss of visual acuity and the size of the visual field. Functional classification that would depict capability to use vision in different activities has not yet been agreed upon. Abnormal visual information leads to changes in visual perception, and brain-damage-related visual impairment may alter or prevent one or several cognitive visual functions. Abnormal visual perception opens a window into brain mechanisms that the psychophysicists otherwise do not have. Together with clinicians, psychophysicists can help visually impaired persons to understand the nature of their disability by thoroughly studying the nature of the altered image and the profile of cognitive visual functions.
Spatial and Contextual Factors in Human Performance on the Travelling Salesperson Problem
Authors: MacGregor James N , Ormerod Thomas C , Chronicle Edward P
Published: November 2005

The travelling salesperson problem (TSP) provides a realistic and practical example of a visuo-spatial problem-solving task. In previous research, we have found that the quality of solutions produced by human participants for small TSPs compares well with solutions from a range of computer algorithms. We have proposed that the ability of participants to find solutions reflects the natural properties of human perception, solutions being found through global perceptual processing of the problem array to extract a best figure from the TSP points. In this paper, we extend the study of human performance on the task in order to understand further how human abilities are utilised in solving real-world TSPs. The results of experiment 1 show that high levels of solution quality are maintained in solving larger TSPs than had been investigated previously with human participants, and that the presence of an implied real-world context in the problems has no effect upon performance. Experiment 2 demonstrated that the presence of regularity in the point layout of a TSP can facilitate performance. This was confirmed in experiment 3, where effects of the internality of point clusters were also found. All three experiments were consistent with a global, perceptually based approach to the problem by participants. We suggest that the role of perceptual processing in spatial problem-solving is an important area for further research in both theoretical and applied domains.
Perceptual and Linguistic Interactions in Speeded Classification: Tests of the Semantic Coding Hypothesis
Authors: Martino Gail , Marks Lawrence E
Published: November 2005

We tested the semantic coding hypothesis, which states that cross-modal interactions observed in speeded classification tasks arise after perceptual information is recoded into an abstract format common to perceptual and linguistic systems. Using a speeded classification task, we first confirmed the presence of congruence interactions between auditory pitch and visual lightness and observed Garner-type interference with nonlinguistic (perceptual) stimuli (low-frequency and high-frequency tones, black and white squares). Subsequently, we found that modifying the visual stimuli by (a) making them lexical (related words) or (b) reducing their compactness or figural ‘goodness’ altered congruence effects and Garner interference. The results are consistent with the semantic coding hypothesis, but only in part, and suggest the need for additional assumptions regarding the role of perceptual organization in cross-modal dimensional interactions.
Veering Re-Visited: Noise and Posture Cues in Walking without Sight
Authors: Millar Susanna
Published: November 2005

Effects of sound and posture cues on veering from the straight-ahead were tested with young blind children in an unfamiliar space that lacked orienting cues. In a pre-test with a previously heard target sound, all subjects walked straight to the target. A recording device, which sampled the locomotor trajectories automatically, showed that, without prior cues from target locations, subjects tended to veer more to the side from which they heard a brief, irrelevant noise. Carrying a load on one side produced more veering to the opposite side. The detailed samples showed that, underlying the main trajectories, were alternating concave and convex (left and right) movements, suggesting stepwise changes in body position. It is argued that the same external and body-centred cues that contribute to reference-frame orientation for locomotion when they converge and concur, influence the direction of veering when the cues occur in isolation in environments that lack converging reference information.
Effects of Eye Size on Adults' Aesthetic Ratings of Faces and 5-Month-Olds' Looking Times
Authors: Geldart Sybil , Maurer Daphne , Carney Katherine
Published: November 2005

In two experiments, we investigated the influence of eye size on adults' ratings of faces' attractiveness and 5-month-olds' looking times. Subjects viewed four pairs of female faces that were identical except for the size of the eyes. Whether they saw black-and-white drawings (experiment 1) or coloured photographs (experiment 2), adults rated the faces with larger eyes as more attractive than the faces with smaller eyes. Babies looked equally long at the drawn faces with larger and smaller eyes (experiment 1), but with the more realistic photographed faces, they looked slightly but significantly longer at the versions with larger eyes (experiment 2). Overall, our results suggest that a modest preference for larger eyes that has emerged by 5 months of age may contribute to the development of adult aesthetic preferences.
Motion Capture of Stationary Lines by Apparently Moving Terminators
Authors: Petersik J Timothy
Published: November 2005

Several studies and observations of a new form of motion capture are reported: frames containing identical rows of evenly spaced vertical lines are alternated in a standard apparent-motion paradigm. However, one vertical line in the first frame has short horizontal ‘terminators’ attached; the terminators are shifted to a different line in the second frame. Alternation that includes an unpatterned, nonzero interstimulus interval results in perceived motion of a vertical line along with the terminators. This motion can ‘cross over’ other stationary vertical lines and persists when light-filled interstimulus intervals and gaps between lines and terminators are introduced. It can also be obtained with different line sizes and spacings. The present motion capture does not appear to rely on a global-frame effect. Alternative explanations are considered.
Effect of Field Size, Head Motion, and Rotational Velocity on Roll Vection and Illusory Self-Tilt in a Tumbling Room
Authors: Allison Robert S , Howard Ian P , Zacher James E
Published: November 2005

The effect of field size, velocity, and visual fixation upon the perception of self-body rotation and tilt was examined in a rotating furnished room. Subjects sat in a stationary chair in the furnished room which could be rotated about the body roll axis. For full-field conditions, complete 360° body rotation (tumbling) was the most common sensation (felt by 80% of subjects). Constant tilt or partial tumbling (less than 360° rotation) occurred more frequently with a small field of view (20 deg). The number of subjects who experienced complete tumbling increased with increases in field of view and room velocity (for velocities between 15 and 30° s−1). The speed of perceived self-rotation relative to room rotation also increased with increasing field of view.
Do Monocular Time-to-Collision Estimates Necessarily Involve Perceived Distance?
Authors: Gray Robert , Regan David
Published: November 2005

Motivated by the debate between indirect and direct theories of perception, a large number of researchers have attempted to determine whether judgments of time to collision are based on the ratio of perceived distance to perceived speed or on the ratio θ/(d θ/d t), ie tau. Despite the considerable research effort devoted to this question there seems to be no clear resolution. We used a staircase tracking procedure to estimate errors in estimating time to collision for a simulated approaching object. To investigate the role of perceived distance in the judgment of time to collision, we asked observers to alternate between two viewing distances (100 and 500 cm). For the 500 cm viewing distance, we magnified the visual display by a factor of five so that the retinal images [and the values of θ/(d θ/d t) through time] were identical for the two viewing distances. All visual cues to distance were available. There were no significant differences between estimates of time to collision made at the two viewing distances. We conclude that our observers ignored perceived distance when estimating time to collision and based their responses on θ/(dθ/d t). We concur with recent proposals that, in the future, time-to-collision research should move away from the either/or analysis of different information sources that has dominated previous studies towards investigations of how different information sources are integrated.
A Limit in the Processing of Components in Odour Mixtures
Authors: Jinks Anthony , Laing David G
Published: November 2005

We investigated the hypothesis that physiological limitations restrict the ability of humans to identify components in an odour mixture. Subjects were trained to identify the test odours, and were required to detect a single highly familiar odorant in stimuli consisting of one, four, eight, twelve, and sixteen odorants by using a selective-attention procedure. The stimuli were delivered by a computer-controlled sixteen-channel air-dilution olfactometer which provided samples of each of the sixteen odorants to be of equal perceived intensity for each subject. Identification fell to chance level when sixteen odorants were present. It is proposed that the profound loss of information was primarily due to inhibition of olfactory receptor cells by the odorants through competitive mechanisms, and the subsequent loss of odour identity through changes in the spatial code that may be used to identify odorants.
Motion Aftereffect of Combined First-Order and Second-Order Motion
Authors: van der Smagt Maarten J , Verstraten Frans A J , Vaessen Eric B P , van Londen Thomas , van de Grind Wim A
Published: November 2005

When, after prolonged viewing of a moving stimulus, a stationary (test) pattern is presented to an observer, this results in an illusory movement in the direction opposite to the adapting motion. Typically, this motion aftereffect (MAE) does not occur after adaptation to a second-order motion stimulus (ie an equiluminous stimulus where the movement is defined by a contrast or texture border, not by a luminance border). However, a MAE of second-order motion is perceived when, instead of a static test pattern, a dynamic test pattern is used. Here, we investigate whether a second-order motion stimulus does affect the MAE on a static test pattern (sMAE), when second-order motion is presented in combination with first-order motion during adaptation. The results show that this is indeed the case. Although the second-order motion stimulus is too weak to produce a convincing sMAE on its own, its influence on the sMAE is of equal strength to that of the first-order motion component, when they are adapted to simultaneously. The results suggest that the perceptual appearance of the sMAE originates from the site where first-order and second-order motion are integrated.
The Influence of Structure from Motion on Motion Correspondence
Authors: Mukai Ikuko , Watanabe Takeo
Published: November 2005

The visual system has a remarkable ability to reconstruct 3-D structure from moving 2-D features. The processing of structure from motion is generally thought to consist of two stages. First, the direction and speed of features is measured (2-D velocity measurement) and, second, 3-D structure is reconstructed from the measured 2-D velocities (3-D structure recovery). Most models have assumed that these stages occur in a bottom – up fashion. Here, however, we present evidence that the 3-D structure-recovery stage influences the 2-D velocity-measurement stage. We developed a stimulus in which two perceptual modes of motion correspondence (one-way translation versus oscillation), and two perceptual modes of 3-D surface structure (flat surface versus cylinder) could be achieved. We found that the likelihood of perceiving both one-way motion and cylindrical structure increased in similar ways with increasing frame duration. In subsequent experiments we found, first, that a higher likelihood of perceiving one-way motion did not affect the likelihood of perceiving cylindrical structure; and, second, that a higher likelihood of perceiving cylindrical structure increased the likelihood of perceiving one-way motion. These results suggest that the higher, 3-D structure-recovery stage may influence the lower, 2-D motion-correspondence stage. This result is not in accordance with most computational models that assume that there is only one-way, feedforward information processing from the 2-D velocity (energy)-measurement stage to the 3-D structure-recovery stage. Perhaps, one of the roles of feedback processing is to seek consensus of the information processed in different stages.
Ecologically Invalid Monocular Texture Leads to Longer Perceptual Latencies in Random-Dot Stereograms
Authors: Grove Philip M , Ono Hiroshi
Published: November 2005

Two experiments were conducted to explore Gillam and Borsting's (1988, Perception17 603–608) report that uncorrelated monocular texture facilitates stereopsis by shortening the latency to see depth in random-dot stereograms. Experiment 1 used stereograms similar, in pattern but not disparity, to Gillam and Borsting's with monocular texture present or absent. A third condition, where monocular texture was dissimilar to the binocular panels and background, was also used. We were unable to generalize the findings of Gillam and Borsting for a depth step of 6 min of arc to a larger depth step of 24 min of arc. That is, we observed no significant difference in latencies between the conditions with monocular texture absent and present at a disparity of 24 min of arc. We found latencies to be significantly longer in the monocular-texture-different condition than the monocular-texture-absent condition, however. We account for this, ad hoc, by arguing that the monocular-texture-different stereogram depicts a rare or ‘accidental’ visual scenario. This account was supported by the results of experiment 2 which showed that stereograms depicting accidental views yielded longer latencies than those depicting generic views. We conclude that the ecological validity of monocular texture must also be considered when assessing the effects of monocular texture on stereopsis.
Collisions between Moving Visual Targets: What Controls Alternative Ways of Seeing an Ambiguous Display?
Authors: Sekuler Allison B , Sekuler Robert
Published: November 2005

When identical visual targets move directly toward and then past one another, they appear either to stream past one another or to bounce off each other. Bertenthal et al (1993 Perception22 193–207) accounted for the relative strengths of these two percepts by invoking a directional bias, arising from cooperative interactions within a network of motion detectors. We tested this explanation by devising conditions that would enhance or diminish the strength of such a directional bias. In separate experiments we varied (i) the presence or absence of temporal transients (pausing, disappearance, occlusion); (ii) the distances travelled by the targets; and (iii) their acceleration or deceleration before and after collision. The tendency to see the objects stream past one another was not related to the strength of an hypothesized directional bias, suggesting that the perception of this ambiguous motion display was not mediated by directional recruitment. Instead, the results suggest that perceived direction reflects the operation of neural constraints that mirror the constraints operating upon moving objects in the three-dimensional natural world.
The Illusory-Letters Phenomenon: An Illustration of Graphemic Restoration in Visual Word Recognition
Authors: Jordan Timothy R , Thomas Sharon M , Scott-Brown Kenneth C
Published: November 2005

We present a demonstration of word perception in which stimuli containing very few letters (just 50% of their original number) are presented for unlimited durations and yet are seen unequivocally as complete words. The phenomenon suggests that recognition of words can be achieved even when perception of their component letters is prevented.
Binocular Rivalry and Visual Awareness: The Role of Attention
Authors: Ooi Teng Leng , He Zijiang J
Published: November 2005

When the right eye and the left eye view dissimilar scenes, the observer does not experience a stable superimposed percept of the images presented to the two eyes, but instead perceives an alternation between the images seen by each eye. A critical question confronting this robust and intriguing phenomenon of binocular rivalry is how the visual system selects the image to be perceived (dominant). The current main-stream literature emphasizes a bottom – up explanation in which the rivalry stimulus with the higher contour strength has the advantage, and becomes dominant in rivalry. Nevertheless, some workers in the past have favored an attention-selection explanation for binocular rivalry. We investigated the role of attention in binocular rivalry by employing novel psychophysical paradigms which capitalized on several established phenomena (eg the Cheshire Cat effect, attention cueing, pop-out effect). Our results revealed two major aspects of attention modulation in binocular rivalry. We found that a dominant image is less likely to be suppressed when voluntary attention is directed to it. This suggests the role of voluntary attention in retaining the dominant image in visual awareness. Second, a rivalry stimulus is more likely to become dominant if accompanied by a pop-out cue (in the same eye and proximity). Since a pop-out cue attracts involuntary attention to its location/eye, this result suggests that cue-mediated involuntary attention can promote the ability of a rivalry stimulus to reach visual awareness.
Encoding ‘Regular’ and ‘Random’ Sequences of Views of Novel Three-Dimensional Objects
Authors: Harman Karin L , Humphrey G Keith
Published: November 2005

When we look at an object as we move or the object moves, our visual system is presented with a sequence of different views of the object. It has been suggested that such regular temporal sequences of views of objects contain information that can aid in the process of representing and recognising objects. We examined whether seeing a series of perspective views of objects in sequence led to more efficient recognition than seeing the same views of objects but presented in a random order. Participants studied images of 20 novel three-dimensional objects rotating in depth under one of two study conditions. In one study condition, participants viewed an ordered sequence of views of objects that was assumed to mimic important aspects of how we normally encounter objects. In the other study condition, participants were presented the same object views, but in a random order. It was expected that studying a regular sequence of views would lead to more efficient recognition than studying a random presentation of object views. Although subsequent recognition accuracy was equal for the two groups, differences in reaction time between the two study groups resulted. Specifically, the random study group responded reliably faster than the sequence study group. Some possible encoding differences between the two groups are discussed.
Stored Representations of three-Dimensional Objects in the Absence of Two-Dimensional Cues
Authors: Phinney Raymond E , Siegel Ralph M
Published: November 2005

Object recognition was studied in human subjects to determine whether the storage of the visual objects was in a two-dimensional or a three-dimensional representation. Novel motion-based and disparity-based stimuli were generated in which three-dimensional and two-dimensional form cues could be manipulated independently. Subjects were required to generate internal representations from motion stimuli that lacked explicit two-dimensional cues. These stored internal representations were then matched against internal three-dimensional representations constructed from disparity stimuli. These new stimuli were used to confirm prior studies that indicated the primacy of two-dimensional cues for view-based object storage. However, under tightly controlled conditions for which only three-dimensional cues were available, human subjects were also able to match an internal representation derived from motion to that of disparity. This last finding suggests that there is an internal storage of an object's representations in three dimensions, a tenet that has been rejected by view-based theories. Thus, any complete theory of object recognition that is based on primate vision must incorporate three-dimensional stored representations.
Haptic Perception of Spatial Relations
Authors: Kappers Astrid M L , Koenderink Jan J
Published: November 2005

There are some indications that haptic space like visual space is not Euclidean (eg Blumenfeld, 1937 Acta Psychologica2 125–174). In a series of experiments, we investigated the haptic perception of spatial relations in a systematic way. We restricted ourselves to a horizontal plane at waist height. Blindfolded subjects were asked to perform three tasks with their right hand: (i) a reference bar was presented under four different orientations and subjects were asked to rotate a test bar such that it felt to be parallel to the reference bar; (ii) subjects had to rotate two test bars in such a way that they felt collinear; (iii) subjects had to point a test bar in the direction of a marker. Bars and marker could appear at nine different locations. In all experiments large systematic deviations (up to 40°) were made. The deviations strongly correlated with horizontal (right-left) but not with vertical (forward-backward) distance. Subjects showed qualitatively identical trends but the size of the deviations was strongly subject-dependent. In addition, a significant haptic oblique effect was found. These results provide strong evidence that haptic space in non-Euclidean.
From Rotation to Disfiguration: Testing a Dual-Strategy Model for Recognition of Faces across View Angles
Authors: Valentin Dominique , Abdi Hervé , Edelman Betty
Published: November 2005

A study is reported of the effect of distinctive marks on the recognition of unfamiliar faces across view angles. Subjects were asked to memorize a set of target faces, half of which had distinctive marks. Recognition was assessed by presenting the target faces, either in the same orientation, or after 90° rotation, mixed with an equal number of distractors. Results show that the effect of distinctive marks depends on the view presented during learning. When a frontal view was learned, as predicted by the dual-strategy model [Valentin et al, in press, in Computational, Geometric, and Process Perspectives on Facial Cognition: Context and Challenges Eds T Wenger, J Townsend (Hillsdale, NJ: Lawrence Erlbaum Associates)], distinctive marks improve recognition performance in the 90° condition but not in the 0° condition. However, when a profile view was learned, distinctive marks have no effect on recognition performance, even in the 90° condition where a frontal view is tested.
The Roles of Vision and Eye Movements in the Control of Activities of Daily Living
Authors: Land Michael , Mennie Neil , Rusted Jennifer
Published: November 2005

The aim of this study was to determine the pattern of fixations during the performance of a well-learned task in a natural setting (making tea), and to classify the types of monitoring action that the eyes perform. We used a head-mounted eye-movement video camera, which provided a continuous view of the scene ahead, with a dot indicating foveal direction with an accuracy of about 1 deg. A second video camera recorded the subject's activities from across the room. The videos were linked and analysed frame by frame. Foveal direction was always close to the object being manipulated, and very few fixations were irrelevant to the task. The first object-related fixation typically led the first indication of manipulation by 0.56 s, and vision moved to the next object about 0.61 s before manipulation of the previous object was complete. Each object-related act that did not involve a waiting period lasted an average of 3.3 s and involved about 7 fixations. Roughly a third of all fixations on objects could be definitely identified with one of four monitoring functions: locating objects used later in the process, directing the hand or object in the hand to a new location, guiding the approach of one object to another (eg kettle and lid), and checking the state of some variable (eg water level). We conclude that although the actions of tea-making are ‘automated’ and proceed with little conscious involvement, the eyes closely monitor every step of the process. This type of unconscious attention must be a common phenomenon in everyday life.
Critical Role of Foreground Stimuli in Perceiving Visually Induced Self-Motion (Vection)
Authors: Nakamura Shinji , Shimojo Shinsuke
Published: November 2005

The effects of a foreground stimulus on vection (illusory perception of self-motion induced by a moving background stimulus) were examined in two experiments. The experiments reveal that the presentation of a foreground pattern with a moving background stimulus may affect vection. The foreground stimulus facilitated vection strength when it remained stationary or moved slowly in the opposite direction to that of the background stimulus. On the other hand, there was a strong inhibition of vection when the foreground stimulus moved slowly with, or quickly against, the background. These results suggest that foreground stimuli, as well as background stimuli, play an important role in perceiving self-motion.
Perceptual Organization of Apparent Motion in the Ternus Display
Authors: He Zijiang J , Ooi Teng Leng
Published: November 2005

A typical Ternus display has three sequentially presented frames, in which frame 1 consists of three motion tokens, frame 2 (blank) defines the interstimulus interval, and frame 3 has similar motion tokens with their relative positions shifted to the right. Interestingly, what appears to be a seemingly simple arrangement of stimuli can induce one of two distinct apparent-motion percepts in the observer. The first is an element-motion perception where the left-end token is seen to jump over its two neighboring tokens (inner tokens) to the right end of the display. The second is a group-motion perception where the entire display of the three tokens is seen to move to the right. How does the visual system choose between these two apparent-motion perceptions? It is hypothesized that the choice of motion perception is determined in part by the perceptual organization of the motion tokens. Specifically, a group-motion perception is experienced when a strong grouping tendency exists among the motion tokens belonging to the same frame. Conversely, an element-motion perception is experienced when a strong grouping tendency exists between the inner motion tokens in frames 1 and 3 (ie the two tokens that overlap in space between frames). We tested this hypothesis by varying the perceptual organization of the motion tokens. Both spatial (form similarity, 3-D proximity, common surface/common region, and occlusion) and temporal (motion priming) factors of perceptual organization were tested. We found that the apparent-motion percept of the Ternus display can be predictably affected, in a manner consistent with the perceptual organization hypothesis.
Effects of the Height of the Internal Features of Faces on Adults' Aesthetic Ratings and 5-Month-Olds' Looking Times
Authors: Geldart Sybil , Maurer Daphne , Henderson Heather
Published: November 2005

We examined the influence of the height of the internal features of faces on adults' ratings of attractiveness and on 5-month-olds' looking times. Subjects viewed drawings or coloured photographs of faces presented in pairs that were identical except that the internal features were at a low height, with a large forehead and small chin; at a high height, with a small forehead and large chin; or at a medium height. Adults rated faces with their features at the medium and low heights as more attractive than faces with their features at the high height, and, at least for drawings, rated faces with medium features as more attractive than faces with low features. Babies looked equally long at faces with their features at various heights except for looking slightly longer at faces with high rather than low features. The results suggest that the influence of feature height on reactions to faces is different for adults and 5-month-olds, and hence that it may be shaped by cultural learning and/or experience with faces sometime after early infancy.
Wakes and Spokes: New Motion-Induced Brightness Illusions
Authors: Holcombe Alex O , Macknik Stephen L , Intriligator James , Seiffert Adriane E , Tse Peter U
Published: November 2005

Under certain conditions, high-contrast moving figures induce adjacent illusory regions, ‘wakes’ and ‘spokes’, which have contrast polarity opposite the inducing figures. In this paper we document properties of these novel phenomena. When the illusions are induced by a moving bar, spokes appear on the side of the bar closer to fixation and connect the bar to the fixation point, regardless of the momentary position of the bar or whether it is moving to the left or to the right. Although spokes often extend up to the fixation point, they never extend beyond it. This is not due to blocking of the spoke's spread by the fixation point, because in another experiment spokes extend directly through an intervening figure. Whereas spokes emanate from the end of a horizontally moving bar closest to fixation, wakes emanate from the end farthest from fixation. In contrast to spokes, wakes do not show a towards-fixation bias. Instead, the wake's end trails the position of the bar, like a ship's wake. The higher the bar velocity, the more the end of the wake appears to trail it, suggesting that wakes are caused by a process which spreads from the edge of moving figures. Wakes and spokes, as distinct illusions, should provide significant constraints on theories of human motion and brightness perception processes.
Recognizing Silhouettes and Shaded Images across Depth Rotation
Authors: Hayward William G , Tarr Michael J , Corderoy Anna K
Published: November 2005

Outline-shape information may be particularly important in the recognition of depth-rotated objects because it provides a coarse shape description which gives first-pass information about the structure of an object. In four experiments, we compared recognition of silhouettes (showing only outline shape) with recognition of fully shaded images of objects, by means of a sequential-matching task. In experiments 1 and 2, the first stimulus was always a shaded image, and the second stimulus was either a shaded image or a silhouette. Recognition costs associated with a change in viewpoint were no greater for silhouettes than they were for shaded images. Experiments 3 and 4 replicated the design of the earlier experiments, but showed a silhouette as the initial stimulus, rather than a shaded image. In these cases, recognition costs associated with a change in viewpoint were greater for silhouettes than for shaded images. Combined, these results indicate that, while visual representations clearly include additional information, outline shape plays an important role in object recognition across depth rotation.
Effects of Face Configuration Change on Shape Perception: A New Illusion
Authors: Lee Kang , Freire Alejo
Published: November 2005

We report two experiments indicating that varying the configuration of face features changes perception of an oval aperture windowing the face: as the eyes and mouth of a frontal-view face photograph are moved vertically toward face boundaries, the oval appears increasingly elongated, taller, and narrower; when eyes and mouth are moved toward the nose, the oval appears increasingly rounder, shorter, and wider. This shape illusion is maximised when faces appear upright within the oval, and major face features (eyes, nose, and mouth) appear in their correct relative locations. These results establish that processing of a face configuration can affect perception of a geometric shape that shares visual space with a face. Whether the illusion is face-specific or a special case of a more general geometric illusion is discussed.
Differences in Top—Down Influences on the Reversal Rate of Different Categories of Reversible Figures
Authors: Strüber Daniel , Stadler Michael
Published: November 2005

Understanding the mechanisms underlying the multistability of reversible figures may provide valuable insights into the normal functioning of our visual system. The proposed factors that control the perceptual alternations of reversible figures can be classified into bottom–up and top–down processes. In the present study, we report differences in top–down effects on the reversal rate depending on whether a structural perspective (Necker cube, Schröder staircase) or a meaningful content (duck/rabbit figure, chef/dog figure) is subject to the reversal phenomenon. In order to activate top–down mechanisms explicitly the subjects had the instruction to bring the reversal rate under voluntary control. The results indicated that both slowing down and speeding up the rate of alternations was more effective for the content-reversal figures (duck/rabbit, chef/dog) than for the rather abstract perspective-reversal figures (Necker cube, Schröer staircase). In order to investigate the effect of meaningfulness in figure/ground reversals, the effect of the same instructional variable was also determined for Rubin's vase/faces and the Maltese cross. The results showed a similar tendency as in the case of the comparison between perspective reversals and content reversals. Possible cognitive processes that may play a role in top–down influences on figure reversal and theoretical implications of these findings for the interaction of bottom–up and top–down processes are discussed.
Motion Parallel to Line Orientation: Disambiguation of Motion Percepts
Authors: Francis Gregory , Kim Hyungjun
Published: November 2005

Four experiments demonstrate that lines indicating path of movement can generate rotational percepts in a multistable motion display that usually produces only horizontal or vertical motion percepts. The properties of the path-of-movement lines are predicted by a neural-network theory of visual perception. Experimental results validate the theory's predictions by demonstrating that movement of the display elements seems to follow an increasing luminance gradient in lines but not bars, and that illusory contours have similar effects. Experimental results also demonstrate that, in a choice between movement along lines drawn parallel or orthogonal to possible motion paths, observers more often see movement along the lines parallel to the motion path. These results suggest modifications to current computational and neurophysiological theories of motion perception.
Analysis of the distribution of light, leaf nitrogen, and photosynthesis within the canopy of Vicia faba L. at two contrasting plant densities
Authors: Del Pozo A. , Dennett M. D.
Published: November 2005

We analysed the spatial variation of irradiance, leaf nitrogen (N)
concentration, specific leaf weight, and photosynthetic capacity of leaves
within canopies of faba bean (Vicia faba var.
minor) grown in the field at 2 contrasting densities (20
and 70 plants/m2), in order to assess whether plant
density can affect the amount of irradiance transmitted, the distribution of
N, and the rate of photosynthesis of leaves within the canopy.
Nitrogen concentration per unit of leaf weight or per unit of leaf area
(Na), and the rate of photosynthesis at saturating
irradiance (Amax), declined from
the upper leaves to the lower, at both plant densities. Plant density had a
strong effect on the extinction coefficients for total irradiance and for
photon flux density (PFD), but little effect on the distribution of
Na. From the relationship between
Na and the cumulative leaf area index, and the fraction
of PFD transmitted through the canopy, it was determined that the coefficient
of leaf N allocation was slightly lower in the high density crop. A similar
curvilinear relationship between
Amax and Na
was found at the 2 plant densities.
Our results indicated that in faba bean a low plant density did not lead to a
more uniform distribution of leaf N through the canopy compared with a high
plant density, as was previously found in other species.
Macro-scale influence of climate on crop production in the Fitzroy catchment of Central Queensland
Authors: Islam F. M. Amirul , Wasimi Saleh A. , Wood Graham R.
Published: November 2005

When the dynamics of a system is too complex to be analytically modelled, it
has been found useful to assume that expected values of explanatory variables
generate expected values of the response variable, and hence, deviations from
the expected value of the response variable can be modelled by a Linear
Perturbation Model (LPM) of the explanatory variables. This method is used in
this study to develop a technique to update crop forecasts where climate is a
major factor in crop production. The study is important because modern
cultivars, which are the result of genetic gains, are sensitive to climatic
variability, and recent studies with general circulation models suggest that
one of the consequences of an increase in greenhouse gases may be greater
variability in the climate of a region.
The usefulness of the LPM technique in the study of agriculture–climate
relationships is tested through application to the Fitzroy catchment in
Central Queensland. Since no reported climatic change is yet occurring in the
region, the expected values for climatic conditions are obtained through
averaging. By contrast, the expected values of crop yield are obtained from
trend analysis; such trends are mainly attributable to genetic gains in the
recent past. Three crops (wheat, barley, and sunflower) have been studied.
Deviations (or perturbations) in crop yields are related, in the framework of
LPM, to deviations in minimum, maximum, and average values of rainfall,
temperature, and humidity at planting, flowering, and harvesting time. The
most significant climatic factors affecting deviations in crop yield are
identified. Regression models are developed which are capable of filtering and
updating crop forecasts due to any unexpected climatic conditions, assuming
consistent genetic trends and management practices.
Phosphorus repletion of cattle previously exposed to dietary nitrogen and phosphorus deficiencies
Authors: Bortolussi G. , Ternouth J. H. , McMeniman N. P.
Published: November 2005

This work reports the effects on growth and metabolic performance of steers
fed 2 levels of phosphorus (P) during their repletion from a 15-week depletion
period when they were fed diets containing various levels of nitrogen (N) and
P. The repletion diets containing either 5·6 g P/day (marginal) or
8·3 g P/day (high) were fed to steers for a period of 12 weeks and
were based on barley straw, molasses, sorghum grain, urea, and
formaldehyde-treated gluten [mean dry matter (DM) digestibility of
0·62 and 14·6 g N/kg DM]. These repletion diets were
formulated to simulate the dietary regimens of cattle grazing wet-season
pastures in northern Australia and other tropical and subtropical regions.
Food intake, liveweight gain, plasma metabolites, and P kinetics were
measured.
There was no significant difference between the repletion marginal- and high-P
treatments in the mean liveweight (LW) gains and DM intakes (g/kg LW) of
the steers. However, for both P treatments, the steers that had been fed a
suboptimal level of N during depletion had marked increases (>60%)
in feed intake throughout the repletion period. Within the marginal-P
treatment, the growth rates of steers that had been fed a suboptimal level of
N during depletion were higher than for those that had been fed higher N
levels, and were similar to those of the high-P groups.
Plasma inorganic P, bone thickness, and bone P concentration remained lower
for the marginal-P treatment at the end of the repletion period. Furthermore,
within the marginal-P treatment, steers that had been fed the high-N diet
during depletion were unable to increase bone thickness and had lower growth
rates than anticipated for the quality of the diet. Although N balance was
positive and similar for both P treatments, the apparent P balance for the
marginal-P treatment of 7·6 mg/kg LW was only about half that of
the high-P treatment. It was concluded that the requirement for dietary P in
steers that had been exposed to a dietary P deficiency, particularly when in
association with high N, was higher than the 5·6 g/day provided.