Divergent mechanisms of perceptual reversals in spinning and wobbling structure-from-motion stimuli.

This study explores the visual phenomenon of random dot structure-from-motion (SFM), where the brain perceives 3D shapes from the coordinated 2D motion of dots. Observing SFM may lead to ambiguous depth relations that reverse back and forth during prolonged viewing. I demonstrate that different processes are involved in triggering perceived reversals for identical SFM shapes involved in spinning and wobbling motion. Durations of stable percepts were measured while human participants viewed the two SFM stimuli, and also a static Necker figure, and a wobbling Necker figure for two sets of 2.5 minutes each. The results showed that wobbling SFM resulted in much longer stable durations compared to the other stimuli. The durations for the wobbling SFM stimuli was not correlated with the spinning SFM, or the two Necker stimuli. Yet, such correlations were obtained between the other stimuli. It is known that reversals obtained while viewing spinning SFM stimuli involves bottom-up driven adaptation and recovery cycles between neural populations. This result suggests that wobbling SFM efficiently deactivates this process and targets other contributions to the reversals, such as top-down processes. In addition, biases observed in the first set disappeared in the second set implying influences of learning between the sets. Imagery vividness, which measures intrinsic top-down processes, was also scored but no correlation between scores in visual imagery and reversal rates were obtained. This research provides insight into the complex interplay between bottom-up driven adaptation-recovery cycles, and top-down processes in ambiguous perception.

Priming and reversals of the perceived ambiguous orientation of a structure-from-motion shape and relation to personality traits.

We demonstrate contributions of top-down and bottom-up influences in perception as explored by priming and counts of perceived reversals and mixed percepts, as probed by an ambiguously slanted structure-from-motion (SFM) test-cylinder. We included three different disambiguated primes: a SFM cylinder, a still image of a cylinder, and an imagined cylinder. In Experiment 1 where the prime and test sequentially occupied the same location, we also administered questionnaires with the Big-5 trait openness and vividness of visual imagery to probe possible relations to top-down driven priming. Since influences of gaze or position in the prime conditions in Experiment 1 could not be ruled out completely, Experiment 2 was conducted where the test cylinder appeared at a randomly chosen position after the prime. In Experiment 2 we also measured the number of perceptual reversals and mixed percepts during prolonged viewing of our ambiguous SFM-cylinder, and administered questionnaires to measure all Big-5 traits, autism, spatial and object imagery, and rational or experiential cognitive styles, associated with bottom-up and top-down processes. The results revealed contributions of position-invariant and cue-invariant priming. In addition, residual contributions of low-level priming was found when the prime and test were both defined by SFM, and were presented at the same location, and the correlation between the SFM priming and the other two priming conditions were weaker than between the pictorial and imagery priming. As previously found with ambiguous binocular rivalry stimuli, we found positive correlations between mixed percepts and the Big-5 dimension openness to experience, and between reversals, mixed percepts and neuroticism. Surprisingly, no correlations between the scores from the vividness of imagery questionnaires and influence from any of the primes were obtained. An intriguing finding was the significant differences between the positive correlation from the experiential cognitive style scores, and the negative correlation between rational style and the cue invariant priming. Among other results, negative correlations between agreeableness and all priming conditions were obtained. These results not only support the notion of multiple processes involved in the perception of ambiguous SFM, but also link these processes in perception to specific personality traits.

Accuracy of conversion formula for effect sizes: A Monte Carlo simulation.

In meta-analysis, effect sizes often need to be converted into a common metric. For this purpose conversion formulas have been constructed; some are exact, others are approximations whose accuracy has not yet been systematically tested. We performed Monte Carlo simulations where samples with pre-specified population correlations between the x and y-variables were drawn from a normally distributed population. A number of commonly used effect size measures and statistics were calculated from each sample. Using several available conversion formula these statistics were converted into Pearson r and Cohen's d and compared to r and d calculated directly from the original data. Converted values were systematically lower than the directly calculated values. While conversions to d were quite accurate, some of the conversions to r resulted in large biases. These systematic errors can in most cases be adjusted for by simply multiplying the converted values with a corresponding correction factor.

Spotting the difference between pairs of nearly identical Perlin images: Influences of presentation formats.

We investigated human performance in speed and precision of detecting a deviating visual target embedded in one of two otherwise identical non-figurative Perlin-noise images (i.e. a spot-the-difference task). The image-pairs were presented in four different presentation formats: spatially separated in horizontal or vertical direction while simultaneously presented, or sequentially separated on the same location with a brief delay or without any delay. In the two spatial conditions failure to detect the target within 30 sec (change blindness) occurred in about 6-7% of the trials, and with the brief delay 2.4% of the trials. Fast error-free detection (i.e. pop out) was obtained using the sequential format with no delay. Average detection time when target was detected was about 9 sec for the two spatial formats. Detection time was faster, about 6 sec, for the brief delay condition. In trials where detection was reported, the precision of locating the target was equal in the horizontal and brief delay conditions, and better than in the vertical condition. Misses obtained in the horizontal and brief delay conditions were also more strongly correlated than correlations between misses in the vertical and horizontal, and between the vertical and brief delay conditions. Some individuals' performances when comparing images in the vertical direction were at chance level. This suggests influences of known poorer precision when making saccades in the vertical compared to horizontal direction. The results may have applications for radiologists since the stimuli and task is similar to radiologists' task when detecting deviations between radiological images.

The behavioral effects of cooperative and competitive board games in preschoolers.

Traditional board games are a common social activity for many children, but little is known about the behavioral effects of this type of game. The current study aims to explore the behavioral effects of cooperative and competitive board games in four-to-six-year-old children (N = 65). Repeatedly during 6 weeks, children in groups of four played either cooperative or competitive board games in a between-subject design, and shortly after each game conducted a task in which children's cooperative, prosocial, competitive, and antisocial behavior were observed. The type of board game did not have an effect on cooperative, prosocial or antisocial behavior. Cooperative and competitive board games elicited equal amounts of cooperative and prosocial behavior, which suggest that board games, regardless of type, could have positive effects on preschoolers' social behavior. Our results suggest that children may compete more after playing competitive board games; but the measure of competitive behavior in particular was unreliable. Preschoolers enjoyed playing cooperative board games more than competitive board games, which may be one reason to prefer their use.

Attentional bias induced by stimulus control (ABC) impairs measures of the approximate number system.

Pervasive congruency effects characterize approximate number discrimination tasks. Performance is better on congruent (the more numerous stimulus consists of objects of larger size that occupy a larger area) than on incongruent (where the opposite holds) items. The congruency effects typically occur when controlling for nonnumeric variables such as cumulative area. Furthermore, only performance on incongruent stimuli seems to predict math abilities. Here, we present evidence for an attentional-bias induced by stimulus control (ABC) where preattentive features such as item size reflexively influence decisions, which can explain these congruency effects. In three experiments, we tested predictions derived from the ABC. In Experiment 1, as predicted, we found that manipulation of size introduced congruency effects and eliminated the correlation with math ability for congruent items. However, performance on incongruent items and neutral, nonmanipulated items were still predictive of math ability. A negative correlation between performance on congruent and incongruent items even indicated that they measure different underlying constructs. Experiment 2 demonstrated, in line with the ABC account, that increasing presentation time reduced congruency effects. By directly measuring overt attention using eye-tracking, Experiment 3 revealed that people direct their first gaze toward the array with items of larger individual size, biasing them towards these arrays. The ABC explains why the relation between performance on approximate number discrimination tasks and math achievement has been fragile and suggests that stimulus control manipulations have contaminated the results. We discuss the importance of using stimuli that are representative of the environment.

Influences of orientation on the Ponzo, contrast, and Craik-O'Brien-Cornsweet illusions.

Explanations of the Ponzo size illusion, the simultaneous contrast illusion, and the Craik-O'Brien-Cornsweet brightness illusions involve either stimulus-driven processes (assimilation, enhanced contrast, and anchoring) or prior experiences. Real-world up-down asymmetries for typical direction of illumination and ground planes in our physical environment should influence these illusions if they are experience based, but not if they are stimulus driven. Results presented here demonstrate differences in illusion strengths between upright and inverted versions of all three illusions. A left-right asymmetry of the Cornsweet illusion was produced by manipulating the direction of illumination, providing further support for the involvement of an experience-based explanation. When the inducers were incompatible with the targets being located at the different distances, the Ponzo illusion persisted and so did the influence from orientation, providing evidence for involvement of processes other than size constancy. As defined here, upright for the brightness illusions is consistent with an interpretation of a shaded bulging surface and a 3D object resulting from a light-from-above assumption triggering compensation for varying illumination. Upright for the Ponzo illusion is consistent with the inducers in the form of converging lines being interpreted as railway tracks receding on the ground triggering size constancy effects. The implications of these results, and other results providing evidence against experience-based accounts of the illusions, are discussed.

Grouping effects in numerosity perception under prolonged viewing conditions.

Humans can estimate numerosities-such as the number sheep in a flock-without deliberate counting. A number of biases have been identified in these estimates, which seem primarily rooted in the spatial organization of objects (grouping, symmetry, etc). Most previous studies on the number sense used static stimuli with extremely brief exposure times. However, outside the laboratory, visual scenes are often dynamic and freely viewed for prolonged durations (e.g., a flock of moving sheep). The purpose of the present study is to examine grouping-induced numerosity biases in stimuli that more closely mimic these conditions. To this end, we designed two experiments with limited-dot-lifetime displays (LDDs), in which each dot is visible for a brief period of time and replaced by a new dot elsewhere after its disappearance. The dynamic nature of LDDs prevents subjects from counting even when they are free-viewing a stimulus under prolonged presentation. Subjects estimated the number of dots in arrays that were presented either as a single group or were segregated into two groups by spatial clustering, dot size, dot color, or dot motion. Grouping by color and motion reduced perceived numerosity compared to viewing them as a single group. Moreover, the grouping effect sizes between these two features were correlated, which suggests that the effects may share a common, feature-invariant mechanism. Finally, we find that dot size and total stimulus area directly affect perceived numerosity, which makes it difficult to draw reliable conclusions about grouping effects induced by spatial clustering and dot size. Our results provide new insights into biases in numerosity estimation and they demonstrate that the use of LDDs is an effective method to study the human number sense under prolonged viewing.

Recent is more: A negative time-order effect in nonsymbolic numerical judgment.

Humans as well as some nonhuman animals can estimate object numerosities-such as the number of sheep in a flock-without explicit counting. Here, we report on a negative time-order effect (TOE) in this type of judgment: When nonsymbolic numerical stimuli are presented sequentially, the second stimulus is overestimated compared to the first. We examined this "recent is more" effect in two comparative judgment tasks: larger-smaller discrimination and same-different discrimination. Ideal-observer modeling revealed evidence for a TOE in 88.2% of the individual data sets. Despite large individual differences in effect size, there was strong consistency in effect direction: 87.3% of the identified TOEs were negative. The average effect size was largely independent of task but did strongly depend on both stimulus magnitude and interstimulus interval. Finally, we used an estimation task to obtain insight into the origin of the effect. We found that subjects tend to overestimate both stimuli but the second one more strongly than the first one. Overall, our findings are highly consistent with findings from studies on TOEs in nonnumerical judgments, which suggests a common underlying mechanism. (PsycINFO Database Record

Individual differences in nonverbal number skills predict math anxiety.

Math anxiety (MA) involves negative affect and tension when solving mathematical problems, with potentially life-long consequences. MA has been hypothesized to be a consequence of negative learning experiences and cognitive predispositions. Recent research indicates genetic and neurophysiological links, suggesting that MA stems from a basic level deficiency in symbolic numerical processing. However, the contribution of evolutionary ancient purely nonverbal processes is not fully understood. Here we show that the roots of MA may go beyond symbolic numbers. We demonstrate that MA is correlated with precision of the Approximate Number System (ANS). Individuals high in MA have poorer ANS functioning than those low in MA. This correlation remains significant when controlling for other forms of anxiety and for cognitive variables. We show that MA mediates the documented correlation between ANS precision and math performance, both with ANS and with math performance as independent variable in the mediation model. In light of our results, we discuss the possibility that MA has deep roots, stemming from a non-verbal number processing deficiency. The findings provide new evidence advancing the theoretical understanding of the developmental etiology of MA.

Arithmetic Training Does Not Improve Approximate Number System Acuity.

The approximate number system (ANS) is thought to support non-symbolic representations of numerical magnitudes in humans. Recently much debate has focused on the causal direction for an observed relation between ANS acuity and arithmetic fluency. Here we investigate if arithmetic training can improve ANS acuity. We show with an experimental training study consisting of six 45-min training sessions that although feedback during arithmetic training improves arithmetic performance substantially, it does not influence ANS acuity. Hence, we find no support for a causal link where symbolic arithmetic training influences ANS acuity. Further, although short-term number memory is likely involved in arithmetic tasks we did not find that short-term memory capacity for numbers, measured by a digit-span test, was effected by arithmetic training. This suggests that the improvement in arithmetic fluency may have occurred independent of short-term memory efficiency, but rather due to long-term memory processes and/or mental calculation strategy development. The theoretical implications of these findings are discussed.

Physiological responses related to moderate mental load during car driving in field conditions.

We measured physiological variables on nine car drivers to capture moderate magnitudes of mental load (ML) during driving in prolonged and repeated city and highway field conditions. Ecological validity was optimized by avoiding any artificial interference to manipulate drivers ML, drivers were alone in the car, they were free to choose their paths to the target, and the repeated drives familiarized drivers to the procedure. Our aim was to investigate if driver's physiological variables can be reliably measured and used as predictors of moderate individual levels of ML in naturally occurring unpredictably changing field conditions. Variables investigated were: heart-rate, skin conductance level, breath duration, blink frequency, blink duration, and eye fixation related potentials. After the drives, with support from video uptakes, a self-rating and a score made by external raters were used to distinguish moderately high and low ML segments. Variability was high but aggregated data could distinguish city from highway drives. Multivariate models could successfully classify high and low ML within highway and city drives using physiological variables as input. In summary, physiological variables have a potential to be used as indicators of moderate ML in unpredictably changing field conditions and to advance the evaluation and development of new active safety systems.

Measuring acuity of the approximate number system reliably and validly: the evaluation of an adaptive test procedure.

Two studies investigated the reliability and predictive validity of commonly used measures and models of Approximate Number System acuity (ANS). Study 1 investigated reliability by both an empirical approach and a simulation of maximum obtainable reliability under ideal conditions. Results showed that common measures of the Weber fraction (w) are reliable only when using a substantial number of trials, even under ideal conditions. Study 2 compared different purported measures of ANS acuity as for convergent and predictive validity in a within-subjects design and evaluated an adaptive test using the ZEST algorithm. Results showed that the adaptive measure can reduce the number of trials needed to reach acceptable reliability. Only direct tests with non-symbolic numerosity discriminations of stimuli presented simultaneously were related to arithmetic fluency. This correlation remained when controlling for general cognitive ability and perceptual speed. Further, the purported indirect measure of ANS acuity in terms of the Numeric Distance Effect (NDE) was not reliable and showed no sign of predictive validity. The non-symbolic NDE for reaction time was significantly related to direct w estimates in a direction contrary to the expected. Easier stimuli were found to be more reliable, but only harder (7:8 ratio) stimuli contributed to predictive validity.

Memory of gender and gait direction from biological motion: gender fades away but directions stay.

The delayed discrimination methodology has been used to demonstrate a high-fidelity nondecaying visual short-term memory (VSTM) for so-called preattentive basic features. In the current Study, I show that the nondecaying high VSTM precision is not restricted to basic features by using the same method to measure memory precision for gait direction and gender-stereotypical gait patterns from high-level point-light walkers. Nondecaying VSTM of direction was found for delays up to 9 s whereas memory for gender decayed. For both tasks, reaction times (RTs) increased with the delay, but only gender RT took longer when the two walkers faced different directions to the line of sight as compared to when they faced the same direction. The results may reflect differences between local and global processes, or an ecologically valid strategy where VSTM resources focus on variables that change, such as tracking people's movements, rather than variables that are constant during short timescales, such as gender.

Motion and color generate coactivation at postgrouping identification stages.

Response times (RTs) were measured in a postgrouping visual identification task. Shapes composed of multiple elements were distinguished by color, motion, orientation, and spatial frequency alone or in pairwise conjunctions. The largest amount of redundancy gain, requiring coactivation as revealed by a race model analysis, was obtained with color-motion conjunctions. In contrast, RTs for a pregrouping detection task using the same target shape as in the identification task, distinguished by color, motion, or a conjunction of these features, showed no evidence for coactivation. The results provide psychophysical evidence for coactivation of color and motion signals in cortical regions specialized for grouping and object identification, as opposed to separate processing of these features in cortical area V1, believed to limit performance in visual search and pregrouping detection.

Visual working memory capacity and stimulus categories: a behavioral and electrophysiological investigation.

It has recently been suggested that visual working memory capacity may vary depending on the type of material that has to be memorized. Here, we use a delayed match-to-sample paradigm and event-related potentials (ERP) to investigate the neural correlates that are linked to these changes in capacity. A variable number of stimuli (1-4) were presented in each visual hemifield. Participants were required to selectively memorize the stimuli presented in one hemifield. Following memorization, a test stimulus was presented that had to be matched against the memorized item(s). Two types of stimuli were used: one set consisting of discretely different objects (discrete stimuli) and one set consisting of more continuous variations along a single dimension (continuous stimuli). Behavioral results indicate that memory capacity was much larger for the discrete stimuli, when compared with the continuous stimuli. This behavioral effect correlated with an increase in a contralateral negative slow wave ERP component that is known to be involved in memorization. We therefore conclude that the larger working memory capacity for discrete stimuli can be directly related to an increase in activity in visual areas and propose that this increase in visual activity is due to interactions with other, non-visual representations.

Integration of colour, motion, orientation, and spatial frequency in visual search.

Response times (RTs) in visual search were measured with either a single target specified by colour, motion, spatial frequency, or orientation alone, or specified by pairwise conjunctions of these features, or by presenting double targets, each specified by a separate feature. First, for all feature combinations, except for motion-colour, RTs were faster when double features were used to specify a single target than when they specified separate targets, implying location-specific redundancy gains predicted by coactivation on a common location-specific map. Second, coactivation, as revealed by race-model violations, occurred for all double-feature single-target conditions except the motion-colour and colour-orientation combinations. No violations occurred in double-target conditions. Taken together, these results are accounted for by well-known feature-specific sensitivities of cortical V1 cells and provide further evidence for a V1 locus of redundancy gain in visual search.

Binding feature dimensions in visual short-term memory.

We explored several possible influences on binding in visual short-term memory (VSTM) performance. The task was to report whether a test object was the same ("old" trials) or different ("new" trials) from any of the sample objects seen a second ago. The objects were composed of two features that varied from continuous to discrete shapes and colors. In "old" trials the test object appeared either in the same or different position. In "new" trials the test object differed along both features, requiring storage of only one feature per object; along one feature, requiring no binding but storage of all features; or it was created by recombining features from the sample, which requires binding. Existing storage hypotheses are unable to explain the similar sensitivity (d') obtained in the two last conditions when position remained the same and may suggest that links are created between positions and features. Highest sensitivity occurred when the test object remained at the same position, required no binding, and discrete features were used. Object-type x position, and feature combination x position interactions occurred, suggesting different storage modes depending on whether objects change position during retention.

Dissociations between slant-contrast and reversed slant-contrast.

A vertical test probe is misperceived as slanted in the opposite direction to an inducer when disparity specifies the inducer slant while monocular cues specify a frontoparallel surface (slant-contrast). In reversed cue conditions with vertical axis slant the test probe is misperceived as slanted in the same direction as the inducer (reversed slant-contrast). We found reliable slant-contrast and reversed slant-contrast with inducers having horizontal-axis slant. The reversed slant-contrast was not influenced when the inducer and probe were separated in the frontal plane or in disparity depth whereas slant contrast was degraded, especially in the latter condition. Slant contrast was most pronounced when the inducer was slanted like a ceiling compared to like a ground. No such difference was found for the reversed slant-contrast. When the cue conflict was minimized slant-contrast was reduced, but only with inducers having ground-like slant. Implications for an existing model explaining the slant effects are discussed.

Liquid-specific stimulus properties can be used for haptic perception of the amount of liquid in a vessel put in motion.

We investigated whether people can use haptic liquid-specific information made available by shaking the vessel containing the liquid. In experiment 1 we studied to what extent people can discriminate between liquid and solid substances and determine the amount of substance in the shaken vessel, as well as the effects of exploratory procedures on these abilities. Exploratory procedures including horizontal shaking of the vessel produced accurate identification of the content and more precise judgments for a liquid than for a solid, but vertical lifting produced an overestimation of the amount of liquid. In experiment 2 we demonstrated that people can discriminate between the amount of liquid and the amount of solid in the same vessel. Three theories of what liquid-specific stimulus properties are picked up by shaking the vessel are preliminarily examined.