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1.  Lustrous material appearances: Internal and external constraints on triggering conditions for binocular lustre 
i-Perception  2014;5(1):1-19.
Lustrous surface appearances can be elicited by simple image configurations with no texture or specular highlights, as most prominently illustrated by Helmholtz' demonstration of stereoscopic lustre. Three types of explanatory framework have been proposed for stereoscopic lustre, which attribute the phenomenon to a binocular luminance conflict, an internalised physical regularity (Helmholtz), or to a disentangling of “essential” and “accidental” attributes in surface representations (Hering). In order to investigate these frameworks, we used haploscopically fused half-images of centre-surround configurations in which the luminances of the test patch were dynamically modulated. Experiment 1 shows that stereoscopic lustre is not specifically tied to situations of a luminance conflict between the eyes. Experiment 2 identifies a novel aspect in the binocular temporal dynamics that provides a physical basis for lustrous appearances, namely the occurrence of a temporal luminance counter-modulation between the eyes. This feature sheds some light on the internal principles underlying a disentangling of “accidental” and “essential” surface attributes. Experiment 3 reveals an asymmetry between a light and a dark reference level for the counter-modulations. This finding again suggests an interpretation in terms of an internalised physical regularity with respect to the dynamics of perceiving illuminated surfaces.
PMCID: PMC4130504  PMID: 25165513
perception of material qualities; lustrous appearances; stereoscopic lustre
2.  Effect of surrounding texture on the pursuit-pursuing illusion 
i-Perception  2014;5(1):20-40.
The pursuit-pursuing illusion is a visual illusion where a circular object placed in the centre of a radial pattern consisting of thin sectors is seen to move in the pursuit eye movement direction. The present study investigates the role of the surrounding texture, replacing the sectors with random dots or stripes in an orientation that was orthogonal, parallel or oblique to the pursuit direction. The experiments demonstrate that the acquired illusory effect was large for the orthogonal stripes. However, each surrounding texture produces a relatively smaller effect than the radial sectors. These results suggest that a hypothesis based on the property of a centre-surround relative-motion detector cannot fully explain the illusion and that the radial stimulus structure itself plays an important role in this illusion.
PMCID: PMC4130505  PMID: 25165514
motion illusion; smooth pursuit; eye movement; relative motion
3.  Motion influences the perception of background lightness 
i-Perception  2014;5(1):41-49.
Uniform backgrounds appear lighter or darker when elements containing luminance gradients move across them, a phenomenon first presented by Ko Nakamura at the 2010 Illusion Contest in Japan. We measured the apparent lightness of the background with a configuration where the grey background was overlaid with moving square patches of vertically oriented luminance gradient. For black-to-grey gradients, the background appeared lighter when the black edges were leading than when they were trailing. For white-to-grey gradients, the background appeared darker when the white edges were leading than when they were trailing. For white-to-black gradients, the background appeared darker with a white edge leading and lighter with a dark edge leading, but the effects were weaker. These results demonstrate that lightness contrast can be modulated by the direction of motion of the inducing patterns. The smooth gradient is essential, because the effect disappeared when the black-to-white gradient was replaced with the binary black and white pattern. We speculate that asymmetry in the processing of a temporal gradient with increasing and decreasing contrast, as proposed to explain the “Rotating Snakes” illusion (Murakami, Kitaoka, & Ashida, 2006, Vision Research, 46, 2421–2431), might be the basis for this effect.
PMCID: PMC4130506  PMID: 25165515
visual illusion; lightness; motion; gradient
4.  Do we need another neural correlate of contour integration? 
i-Perception  2014;5(1):50-52.
Gilad and colleagues use an elegant combination of voltage-sensitive dyes and high temporal and spatial resolution optical imaging to visualize a differential response to collinear contour elements in monkey V1. This result adds to the literature on the neural correlates of contour integration, but does not yet tackle (or seek to tackle) the question as to whether contour integration is mediated by lateral connections within an area (e.g., V1), through pooling of feedfoward connections, or feedback mechanisms. Moreover, while Gilad et al. find that their differential response is correlated with the behavioral performance of each monkey, there are reasons to suspect that the correlation they observe is a consequence of processing in higher regions, and that the differential V1 response may not play a critical role in integrating contour elements, or in generating the monkey's response. Moreover, this differential V1 response was not observed in a monkey who was not trained on the task, a result that can only be reconciled, if one assumes that the monkey could not see the contour prior to training. If valid, this could raise doubts as to whether the study of contour integration really provides insights into the processes by which normal visual perception is achieved.
PMCID: PMC4130507  PMID: 25165516
contour integration; neural correlate; perception; lateral connections; pooling; feedback
5.  Scaling measurements of the effect of surface slant on perceived lightness 
i-Perception  2014;5(1):53-72.
The light reflected from an object depends on its reflectance, the illumination, and the pose of the object within the scene. An observer is called lightness constant if the perceived reflectance (lightness) of achromatic objects stays the same despite variation in object-extrinsic factors such as illumination and pose. Here, we used a dissimilarity scaling task to measure lightness constancy as the intensity of the illuminant and the slant of test surfaces were varied. Across two experiments, we had observers rate the dissimilarity of flat grayscale test stimulus pairs. The test stimuli were real illuminated surfaces, not computer simulations. Each test stimulus was seen in its own illuminated chamber, with the two chambers viewed side by side. We varied test surface reflectance, chamber illumination intensity, and the slant of the test in relation to the single light source in each chamber. Data were analyzed using nonmetric multidimensional scaling. The data were well-described by a one-dimensional perceptual representation. This representation was consistent across observers, revealed partial lightness constancy with respect to a change in illumination intensity, and no lightness constancy with respect to changes in surface slant. An additional experiment using a matching procedure and the same stimulus set, however, revealed moderate constancy with respect to changes in surface slant. The difference in results between the two methods is interesting, but not understood.
PMCID: PMC4130508  PMID: 25165517
lightness constancy; multidimensional scaling; surface perception; perceptual representation
6.  Pattern specificity of contrast adaptation 
i-Perception  2014;5(1):73-74.
Contrast adaptation is specific to precisely localised edges, so that adapting to a flickering photograph makes one less sensitive to that same photograph, but not to similar photographs. When two low-contrast photos, A and B, are transparently superimposed, then adapting to a flickering high-contrast B leaves no net afterimage, but it makes B disappear from the A+B picture, which now simply looks like A.
PMCID: PMC4130509  PMID: 25165518
adaptation; flicker; contrast; contour
7.  Sharing code 
i-Perception  2014;5(1):75-78.
Sharing code is becoming increasingly important in the wake of Open Science. In this review I describe and compare two popular code-sharing utilities, GitHub and Open Science Framework (OSF). GitHub is a mature, industry-standard tool but lacks focus towards researchers. In comparison, OSF offers a one-stop solution for researchers but a lot of functionality is still under development. I conclude by listing alternative lesser-known tools for code and materials sharing.
PMCID: PMC4130510  PMID: 25165519
code sharing; github; open science framework; open science; version control
8.  The effects of social misdirection on magic tricks: How deceived and undeceived groups differ 
i-Perception  2014;5(3):143-146.
Characteristics of perception and cognition in our daily lives can be elucidated through studying misdirection, a technique used by magicians to manipulate attention. Recent findings on the effects of social misdirection induced by joint attention have been disputed, and differences between deceived (failed to detect the magic trick) and undeceived (detected the magic trick) groups remain unclear. To examine how social misdirection affects deceived and undeceived groups, we showed participants movie clips of the “cups & balls,” a classic magic trick, and measured participants' eye positions (i.e. where participants looked while viewing the clips) using an eye tracker. We found that the undeceived group looked less at the magician's face than the deceived group. These results indicate that deceived individuals have difficulty trying not to allocate attention to the face. We conclude that social misdirection captures attention, influencing the emergence of deception.
PMCID: PMC4249983  PMID: 25469219
eye movements; magic trick; misdirection; social misdirection; visual attention
9.  Attention modulation of stimulus rivalry under swapping paradigm 
i-Perception  2014;5(3):147-152.
Stimulus rivalry refers to the sustained periods of perceptual dominance that occur when different visual stimuli are swapped at a regular rate between eyes. This phenomenon is thought to involve mainly eye-independent mechanisms. Although several studies have reported that attention can increase image predominance in conventional binocular rivalry, it is unknown whether attention can specifically modulate stimulus rivalry. We addressed this question and manipulated the spatial characteristic of the stimuli to assess whether such an attention modulation could depend on visual processing hierarchy. The results showed that selective attention of stimulus rivalry significantly increased the predominance of the attended stimulus, regardless of the stimulus' spatial characteristics. No effect was observed on the swapping percept. The findings are discussed in the context of recent models attempting to characterize stimulus rivalry between eye-dependent and eye-independent levels.
PMCID: PMC4249984  PMID: 25469220
attention; binocular rivalry; stimulus rivalry; eye-dependent mechanisms; eye-independent mechanisms
10.  Vigorous orientation signal propagates best from collinear motion 
i-Perception  2014;5(3):164-169.
In the present study, the Poggendorff illusion was tested with four types of stimuli: A moving dot, a moving bar parallel to the inducing lines, a moving bar collinear to the motion trajectory, and static bars as in the classic illusion. Psychometric functions of the alignment task showed that the collinear bar, where orientation and motion trajectory matched, yielded the best alignment performance almost eliminating the illusion; the vertical bar, on the contrary, showed the worst alignment, finally the dot and the static bars led to intermediate alignments. These results demonstrate the interaction between orientation and motion trajectory that likely takes place in the primary visual cortex (V1) where these two signals might be modulated by top-down activity from higher order areas such as the middle temporal (MT). This vigorous orientation-motion trajectory interaction allows extremely accurate positional predictions of moving objects in the visual scene, in particular during occlusion.
PMCID: PMC4249986  PMID: 25469222
collinear context; Poggendorff illusion; visual motion; context modulation; orientation-motion trajectory interaction; V1-MT
11.  Probability cueing influences miss rate and decision criterion in visual searches 
i-Perception  2014;5(3):170-175.
In visual search tasks, the ratio of target-present to target-absent trials has an important effect on miss rates. The low prevalence effect indicates that we are more likely to miss a target when it occurs rarely rather than frequently. In this study, we examined whether probability cueing modulates the miss rate and the observer's criterion. The results indicated that probability cueing affects miss rates, the average observer's criterion, and reaction time for target-absent trials. These results clearly demonstrate that probability cueing modulates two parameters (i.e., the decision criterion and the quitting threshold) and produces a low prevalence effect. Taken together, the current study and previous studies suggest that the miss rate is not just affected by global prevalence; it is also affected by probability cueing.
PMCID: PMC4249987  PMID: 25469223
visual search; low prevalence effect; probability cueing
12.  Why am I not photogenic? Differences in face memory for the self and others 
i-Perception  2014;5(3):176-187.
Many people complain that they do not photograph well. In the present study, we hypothesised that the self-face is memorized more beautifully than reality, which may result in reports of being not photogenic. We took photographs of students who were in the same university course and were familiar with one another. We then magnified or shrunk the size of their eyes (Experiment 1; N = 10) and their mouths (Experiment 2; N = 10). We asked the students to select the picture that seemed most like their classmates' real faces or their own real face. The results showed that there were significant differences between memories of their own and others' faces. Participants selected their classmates' real faces to a greater degree than the modified faces. However, participants tended to select pictures of themselves with magnified eyes and shrunken mouths more often than for their classmates. In Experiment 3 (N = 22), more male participants were included and the influence of gender and mirror-reversed images were examined. We found that there were no significant differences across gender, and the mirror reversal did not change the participants' selections. The bias of self-face recognition may reflect different memory processes for the self and others.
PMCID: PMC4249988  PMID: 25469224
face recognition; self-face; familiar face; positive evaluation; beauty; gender differences
13.  Local shape of pictorial relief 
i-Perception  2014;5(3):188-204.
How is pictorial relief represented in visual awareness? Certainly not as a “depth map,” but perhaps as a map of local surface attitudes (Koenderink & van Doorn, 1995). Here we consider the possibility that observers might instead, or concurrently, represent local surface shape, a geometrical invariant with respect to motions. Observers judge local surface shape, in a picture of a piece of sculpture, on a five-point categorical scale. Categories are cap–ridge–saddle–rut–cup–flat, where “flat” denotes the absence of shape. We find that observers readily perform such a task, with full resolution of a shape index scale (cap–ridge–saddle–rut–cup), and with excellent self-consistency over days. There exist remarkable inter-observer differences. Over a group of 10 naive observers we find that the dispersion of judgments peaks at the saddle category. There may be a relation of this finding to the history of the topic—Alberti's (1827) omission of the saddle category in his purportedly exhaustive catalog of local surface shapes.
PMCID: PMC4249989  PMID: 25469225
shape perception; surface perception; picture perception; depth perception; shape scale
14.  Drawing skill is related to the efficiency of encoding object structure 
i-Perception  2014;5(2):101-119.
Accurate drawing calls on many skills beyond simple motor coordination. A good internal representation of the target object's structure is necessary to capture its proportion and shape in the drawing. Here, we assess two aspects of the perception of object structure and relate them to participants' drawing accuracy. First, we assessed drawing accuracy by computing the geometrical dissimilarity of their drawing to the target object. We then used two tasks to evaluate the efficiency of encoding object structure. First, to examine the rate of temporal encoding, we varied presentation duration of a possible versus impossible test object in the fovea using two different test sizes (8° and 28°). More skilled participants were faster at encoding an object's structure, but this difference was not affected by image size. A control experiment showed that participants skilled in drawing did not have a general advantage that might have explained their faster processing for object structure. Second, to measure the critical image size for accurate classification in the periphery, we varied image size with possible versus impossible object tests centered at two different eccentricities (3° and 8°). More skilled participants were able to categorise object structure at smaller sizes, and this advantage did not change with eccentricity. A control experiment showed that the result could not be attributed to differences in visual acuity, leaving attentional resolution as a possible explanation. Overall, we conclude that drawing accuracy is related to faster encoding of object structure and better access to crowded details.
PMCID: PMC4249990  PMID: 25469216
artists; drawing accuracy; expertise; object structure; object perception; impossible objects
15.  Seeing the world topsy-turvy: The primary role of kinematics in biological motion inversion effects 
i-Perception  2014;5(2):120-131.
Physical inversion of whole or partial human body representations typically has catastrophic consequences on the observer's ability to perform visual processing tasks. Explanations usually focus on the effects of inversion on the visual system's ability to exploit configural or structural relationships, but more recently have also implicated motion or kinematic cue processing. Here, we systematically tested the role of both on perceptions of sex from upright and inverted point-light walkers. Our data suggest that inversion results in systematic degradations of the processing of kinematic cues. Specifically and intriguingly, they reveal sex-based kinematic differences: Kinematics characteristic of females generally are resistant to inversion effects, while those of males drive systematic sex misperceptions. Implications of the findings are discussed.
PMCID: PMC4249991  PMID: 25469217
biological motion; sex perception; inversion; point-light walkers; structural processing; kinematic processing
16.  Cross-modal associations in synaesthesia: Vowel colours in the ear of the beholder 
i-Perception  2014;5(2):132-142.
Human speech conveys many forms of information, but for some exceptional individuals (synaesthetes), listening to speech sounds can automatically induce visual percepts such as colours. In this experiment, grapheme–colour synaesthetes and controls were asked to assign colours, or shades of grey, to different vowel sounds. We then investigated whether the acoustic content of these vowel sounds influenced participants' colour and grey-shade choices. We found that both colour and grey-shade associations varied systematically with vowel changes. The colour effect was significant for both participant groups, but significantly stronger and more consistent for synaesthetes. Because not all vowel sounds that we used are “translatable” into graphemes, we conclude that acoustic–phonetic influences co-exist with established graphemic influences in the cross-modal correspondences of both synaesthetes and non-synaesthetes.
PMCID: PMC4249992  PMID: 25469218
coloured vowels; cross-modal perception; colour vision; synaesthesia; vowel sounds
17.  Contour erasure and filling-in: New observations 
i-Perception  2014;5(2):79-86.
Contour erasure is a newly established form of flicker adaptation that diminishes the saliency of object edges leading to their complete disappearance (Anstis, S. 2013. Journal of Vision, 13(2):25, 1–14). If these “disappeared” objects are then viewed on textured backgrounds, the observers experience filling-in, the illusory sense of background completion in the absence of physical input. In a series of observations, we demonstrate that contour erasure can greatly speed up the filling-in (or fading) of brightness. Based on these observations, we suggest that contour adaptation happens early in the magnocellular pathways.
PMCID: PMC4249993  PMID: 25469212
contour adaptation; filling-in; brightness perception; object completion; Troxler fading
18.  Shape recognition elicited by microsecond flashes is not based on photon quantity 
i-Perception  2014;5(2):87-93.
It is generally thought that the perceptual impact of a brief flash of light is determined by the quantity of photons the flash delivers. This means that only the total quantity of photons is important below a critical duration of about 30–100 ms. Recent findings have challenged this concept and the present work provides additional evidence that it is not correct. The first experiment reported here delivered a given quantity of photons in under 200 μs, either as a single threshold-intensity flash or as multiple flashes at the same intensity. The single flash was ineffective at eliciting recognition, but multiple flashes became progressively more effective as the number of flashes was increased. A second experiment varied the number of 10 μs flashes. The effectiveness of multiple flashes was far higher than would be expected on the basis of the total quantity of photons being delivered. The results of both experiments suggest that the brief transitions of intensity provided by the flashes are far more important than the quantity of photons. A final experiment examined the combined impact from two threshold-intensity flashes as the interstimulus interval was increased. The pair members were able to combine their influence for at least 100 ms. These results call for more attention to how very brief light flashes generate signals that convey image content.
PMCID: PMC4249994  PMID: 25469213
shape recognition; brief flashes; Bloch's Law; information persistence
19.  Recent evidence on perception and esthetic appreciation: The role of value and expertise in canon formation 
i-Perception  2014;5(2):94-96.
On the basis of current evidence derived from neurocognitive research, it is possible to mediate two alternative theories concerning the relationship between perception and esthetic appreciation, in particular by distinguishing between high-quality images and popular.
PMCID: PMC4249995  PMID: 25469214
images; (dis)fluency; (un)predictability; appreciation; canon; expertise
20.  Upper visual field advantage in localizing a target among distractors 
i-Perception  2014;5(2):97-100.
Biases exist in many perceptual and cognitive functions. Since visual attention plays an important role in a wide range of perceptual and cognitive processes, any bias in the spatial distribution of attention is likely to be a significant source of perceptual and cognitive asymmetries. An attentional visual field task (AVF) requiring localization of a target among distractors was used to assess possible asymmetries in attentional processing in the vertical meridian. The results showed a bias favoring the upper visual field, suggesting a potentially important role of attention in perceptual and cognitive asymmetries.
PMCID: PMC4249996  PMID: 25469215
spatial attention; distribution of attention; attentional bias; individual difference
21.  Modifying action sounds influences people's emotional responses and bodily sensations 
i-Perception  2014;5(3):153-163.
We report an experiment designed to investigate the effect of modifying the sound of high-heeled shoes on women's self-reported valence, arousal, and dominance scores, as well as any changes to a variety of measures of bodily sensation. We also assessed whether self-evaluated personality traits and the enjoyment associated with wearing heels were correlated with these effects. Forty-eight women walked down a “virtual runway” while listening to four interaction sounds (leather- and polypropylene-soled high-heeled shoes contacting ceramic flooring or carpet). Analysis of the questionnaires that the participants completed indicated that the type of sonic interaction impacted valence, arousal, and dominance scores, as well as the evaluated bodily sensations. There were also correlations between these scores and both self-evaluated personality traits and the reported enjoyment associated with wearing high heels. These results demonstrate the effect that the sound of a woman's physical interaction with the environment can have, especially when her contact with the ground while walking makes a louder sound. More generally, these results demonstrate that the manipulation of product extrinsic sounds can modify people's evaluation of their emotional outcomes (valence, arousal, and dominance), as well as their bodily sensations.
PMCID: PMC4249985  PMID: 25469221
multisensory perception; auditory perception; sonic interaction; user experience; consumer behaviour
22.  The binocular advantage in visuomotor tasks involving tools 
i-Perception  2013;4(2):101-110.
We compared performance on three manual-dexterity tasks under monocular and binocular viewing. The tasks were the standard Morrisby Fine Dexterity Test, using forceps to manipulate the items, a modified version of the Morrisby test using fingers, and a “buzz-wire” task in which subjects had to guide a wire hoop around a 3D track without bringing the hoop into contact with the track. In all three tasks, performance was better for binocular viewing. The extent of the binocular advantage in individuals did not correlate significantly with their stereoacuity measured on the Randot test. However, the extent of the binocular advantage depended strongly on the task. It was weak when fingers were used on the Morrisby task, stronger with forceps, and extremely strong on the buzz-wire task (fivefold increase in error rate with monocular viewing). We suggest that the 3D buzz-wire game is particularly suitable for assessing binocularly based dexterity.
PMCID: PMC3677330  PMID: 23755355
binocular vision; stereoscopic depth perception; visuomotor skills; dexterity; motor coordination
23.  Perception of length to width relations of city squares 
i-Perception  2013;4(2):111-121.
In this paper, we focus on how people perceive the aspect ratio of city squares. Earlier research has focused on distance perception but not so much on the perceived aspect ratio of the surrounding space. Furthermore, those studies have focused on “open” spaces rather than urban areas enclosed by walls, houses and filled with people, cars, etc. In two experiments, we therefore measured, using a direct and an indirect method, the perceived aspect ratio of five city squares in the historic city center of Delft, the Netherlands. We also evaluated whether the perceived aspect ratio of city squares was affected by the position of the observer on the square. In the first experiment, participants were asked to set the aspect ratio of a small rectangle such that it matched the perceived aspect ratio of the city square. In the second experiment, participants were asked to estimate the length and width of the city square separately. In the first experiment, we found that the perceived aspect ratio was in general lower than the physical aspect ratio. However, in the second experiment, we found that the calculated ratios were close to veridical except for the most elongated city square. We conclude therefore that the outcome depends on how the measurements are performed. Furthermore, although indirect measurements are nearly veridical, the perceived aspect ratio is an underestimation of the physical aspect ratio when measured in a direct way. Moreover, the perceived aspect ratio also depends on the location of the observer. These results may be beneficial to the design of large open urban environments, and in particular to rectangular city squares.
PMCID: PMC3677331  PMID: 23755356
scene perception; vision; public spaces; city squares; space perception
24.  The role of binocular disparity in rapid scene and pattern recognition 
i-Perception  2013;4(2):122-136.
We investigated the contribution of binocular disparity to the rapid recognition of scenes and simpler spatial patterns using a paradigm combining backward masked stimulus presentation and short-term match-to-sample recognition. First, we showed that binocular disparity did not contribute significantly to the recognition of briefly presented natural and artificial scenes, even when the availability of monocular cues was reduced. Subsequently, using dense random dot stereograms as stimuli, we showed that observers were in principle able to extract spatial patterns defined only by disparity under brief, masked presentations. Comparing our results with the predictions from a cue-summation model, we showed that combining disparity with luminance did not per se disrupt the processing of disparity. Our results suggest that the rapid recognition of scenes is mediated mostly by a monocular comparison of the images, although we can rely on stereo in fast pattern recognition.
PMCID: PMC3677332  PMID: 23755357
stereo vision; natural image; scene recognition; random-dot stereogram; visual masking
25.  On why music changes what (we think) we taste 
i-Perception  2013;4(2):137-140.
A pair of recently published studies demonstrate that what we happen to be listening to can sometimes change our perception (or, at the very least, our rating) of what we are eating or drinking. In one recent study, North (2012) showed that the emotional attributes (or connotation) of a piece of music could influence people's perception of red or white wine. Meanwhile, Crisinel et al. (2012) reported that listening to a lower-pitched soundscape can help to emphasize the bitter notes in a bittersweet toffee while listening to a soundscape with a higher pitch tends to bring out its sweetness. Although the most appropriate psychological and neuroscientific explanations for such crossmodal effects are still uncertain, we outline a number of possible alternatives for such intriguing, not to mention surprising, phenomena.
PMCID: PMC3677333  PMID: 23755358
music; flavour; taste; crossmodal correspondences; crossmodal effects

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