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  • 1. af Wahlberg, A. E.
    et al.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    An Empirical Test of Nonresponse Bias in Internet Surveys2015In: Basic and Applied Social Psychology, ISSN 0197-3533, E-ISSN 1532-4834, Vol. 37, no 6, p. 336-347Article in journal (Refereed)
    Abstract [en]

    In surveys, nonresponse is considered a source of possible bias, which increases with the size of the nonresponding group. Nonresponse bias was investigated in 3 samples of offending drivers who were required to respond to an online questionnaire before taking a driver improvement course, creating an initial 100% response rate. The next 2 questionnaire waves were voluntary, and response rates were much lower. Results (means, internal consistency, correlations, etc.) in the first wave were compared between those who responded twice or thrice and those who responded only to the first wave. No substantial differences were found. Compared to common method variance, the effects of nonresponse are very small.

  • 2.
    Börjesson, Erik
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Visual slant-contrast across space and attributes2002In: Journal of Vision, ISSN 1534-7362, E-ISSN 1534-7362, Vol. 2, no 7, p. 91a-Article in journal (Other academic)
  • 3.
    Diamantopoulou, Sofia
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Klaver, Peter
    Talsma, Durk
    Visual working memory capacity and stimulus categories: a behavioral and electrophysiological investigation2011In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 209, no 4, p. 501-513Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Jansson, Gunnar
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Juslin, Peter
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Liquid-specific stimulus properties can be utilized for haptic perception of amount of liquid in a vessel put in motion.2006In: Perception, ISSN 0301-0066, E-ISSN 1468-4233, Vol. 35, no 10, p. 1421-32Article in journal (Refereed)
  • 5.
    Lindskog, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Juslin, Peter
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Measuring acuity of the approximate number system reliably and validly: the evaluation of an adaptive test procedure2013In: Frontiers in Psychology, ISSN 1664-1078, E-ISSN 1664-1078, Vol. 4, p. 510-Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Lindskog, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Arithmetic Training Does Not Improve Approximate Number System Acuity2016In: Frontiers in Psychology, ISSN 1664-1078, E-ISSN 1664-1078, Vol. 7, article id 1634Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Lindskog, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Can approximate number system acuity improve with arithmetic training?2014Conference paper (Refereed)
  • 8.
    Lindskog, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Individual differences in nonverbal number skills predict math anxiety2017In: Cognition, ISSN 0010-0277, E-ISSN 1873-7838, Vol. 159, p. 156-162Article in journal (Refereed)
    Abstract [en]

    Abstract 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.

  • 9.
    Lindskog, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    While waiting for the dots: The influence of short-term memory in tasks indexing the Approximate Number System?2014Conference paper (Refereed)
  • 10.
    Olsson, Henrik
    et al.
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    The noisy cue abstraction model is equivalent to the multiplicative prototype model.2005In: Perceptual and Motor Skills, ISSN 0031-5125, Vol. 100, no 3 Pt 1, p. 819-20Article in journal (Refereed)
    Abstract [en]

    We prove that the noisy cue abstraction model for binary choice and the multiplicative prototype model of categorization are formally identical.

  • 11.
    Olsson, Henrik
    et al.
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Visual memory needs categories2005In: Proceedings of the National Academy of Sciences USA, ISSN 0027-8424, Vol. 102, no 24, p. 8776-80Article in journal (Refereed)
    Abstract [en]

    Capacity limitations in the way humans store and process information in working memory have been extensively studied, and several memory systems have been distinguished. In line with previous capacity estimates for verbal memory and memory for spatial information, recent studies suggest that it is possible to retain up to four objects in visual working memory. The objects used have typically been categorically different colors and shapes. Because knowledge about categories is stored in long-term memory, these estimations of working memory capacity have been contaminated by long-term memory support. We show that when using clearly distinguishable intracategorical items, visual working memory has a maximum capacity of only one object. Because attention is closely involved in the working memory process, our results add to other studies demonstrating capacity limitations of human attention such as inattentional blindness and change blindness.

  • 12.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Inter-attribute tilt effects and orientation analysis in the visual brain2000In: Vision Research, ISSN 0042-6989, E-ISSN 1878-5646, Vol. 40, no 20, p. 2711-2722Article in journal (Refereed)
    Abstract [en]

    A test grating appears to be tilted away from an inducing grating for small angular separations (repulsion), but towards the inducing grating for larger angular separations (attraction). Previous research on luminance gratings suggests that repulsion is c

  • 13.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Inter-attribute tilt effects and orientation analysis in the visual brain2000In: Vision Research, ISSN 0042-6989, E-ISSN 1878-5646, Vol. 40, no 20, p. 2711-2722Article in journal (Refereed)
    Abstract [en]

    A test grating appears to be tilted away from an inducing grating for small angular separations (repulsion), but towards the inducing grating for larger angular separations (attraction). Previous research on luminance gratings suggests that repulsion is caused by local inhibition in cortical areas V1 and/or V2, and that the attraction involves global interactions beyond V1, in extrastriate areas. Experiments reported here demonstrate attribute invariant attraction and repulsion effects for gratings specified by luminance, motion, and disparity contrasts. A frame surrounding the inducing grating abolishes only the attraction effect, but a spatial frequency difference, or a small gap between the inducer and test gratings, abolishes only the repulsion effect, irrespective of the attributes that specify the gratings. It is proposed that detectors selectively sensitive to attribute invariant orientation and size exist in early cortical sites such as V1 and/or V2.

  • 14.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Mechanisms for seeing transparency-from-motion and orientation-from-motion2000In: Perception, ISSN 0301-0066, E-ISSN 1468-4233, Vol. 29, no 6, p. 661-674Article in journal (Refereed)
    Abstract [en]

    Structure-from-motion (SFM) perception is hypothesised to be mediated by units that sense the near-far relationships in transparency-from-motion (TFM) and orientation-from-motion (OFM). The frequency of subjective reversals during observation of ambiguous

  • 15.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Memory of Gender and Gait Direction From Biological Motion: Gender Fades Away But Directions Stay2012In: Journal of Experimental Psychology: Human Perception and Performance, ISSN 0096-1523, E-ISSN 1939-1277, Vol. 38, no 5, p. 1091-1097Article in journal (Refereed)
    Abstract [en]

    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.

  • 16.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Motion and color generate coactivation at postgrouping identification stages2011In: Attention, Perception & Psychophysics, ISSN 1943-3921, E-ISSN 1943-393X, Vol. 73, no 6, p. 1833-1842Article in journal (Refereed)
    Abstract [en]

    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.

  • 17.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Seeing stereoscopic depth from disparity between kinetic edges2002In: Perception, ISSN 0301-0066, E-ISSN 1468-4233, Vol. 31, no 12, p. 1439-1448Article in journal (Refereed)
  • 18.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Visual binding of luminance, motion, and disparity edges2002In: Vision Research, ISSN 0042-6989, E-ISSN 1878-5646, Vol. 42, no 23, p. 2577-2591Article in journal (Refereed)
    Abstract [en]

    Visual binding of edge segments embedded in noise and created by luminance, motion and disparity contrasts were studied in three experiments. The results showed that path formation was limited by the same rules across all attributes tested. The first experiment showed that binding could be accomplished with either attribute used in isolation. The second experiment showed that closed paths were easier to detect than open paths irrespectively of the attributes used to create the path elements. No additive effects were found in either Experiment 1 or 2 when the path elements were created with several attributes superimposed on the same positions, compared to when only one attribute was used along the path. In Experiment 3 it was found that when another attribute was added between the positions of the first attribute along the path, so that two attributes alternated along the path, the performance of path detection was better than expected by probability summation estimated from the single attribute conditions. These results provide evidence for attribute-invariant Gestalt laws and provide clues about the underlying neural mechanisms.

  • 19.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Visual inter-attribute contour completion2001In: Perception, ISSN 0301-0066, E-ISSN 1468-4233, Vol. 30, no 7, p. 855-865Article in journal (Refereed)
    Abstract [en]

    A new visual phenomenon, inter-attribute illusory (completed) contours, is demonstrated. Contour completions are perceived between any combination of spatially separate pairs of inducing elements (Kanizsa-like 'pacman' figures) defined either by pictorial

  • 20.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Visual summation of luminannce lines and illusory contours induced by pictorial, motion, and disparity cues2001In: Vision Research, ISSN 0042-6989, E-ISSN 1878-5646, Vol. 41, no 28, p. 3805-3816Article in journal (Refereed)
  • 21.
    Poom, Leo
    et al.
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Börjesson, Erik
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Colour, polarity, disparity, and texture contributions to motion segregation.2005In: Perception, ISSN 0301-0066, Vol. 34, no 10, p. 1193-203Article in journal (Refereed)
  • 22.
    Poom, Leo
    et al.
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Börjesson, Erik
    Uppsala University, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Faculty of Social Sciences, Department of Psychology.
    Good continuation with kinetic edges.2004In: Vision Res, ISSN 0042-6989, Vol. 44, no 18, p. 2101-8Article in journal (Other scientific)
  • 23.
    Poom, Leo
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Börjesson, Erik
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Perceptual depth synthesis in the visual system as revealed by selective adaptation1999In: Journal of Experimental Psychology: Human Perception and Performance, ISSN 0096-1523, E-ISSN 1939-1277, Vol. 25, no 2, p. 504-517Article in journal (Refereed)
    Abstract [en]

    Selective adaptation was used to determine the degree of interactions between channels processing relative depth from stereopsis. motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surf

  • 24.
    Poom, Leo
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Lindskog, Marcus
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Van den Berg, Ronald
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Grouping effects in numerosity perception under prolonged viewing conditions2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 2, article id e0207502Article in journal (Refereed)
    Abstract [en]

    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.

  • 25.
    Poom, Leo
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Löfroth, Claes
    Nordén, Berndt
    Testing human visual detection with xenon and halogen lamps as used on forest machines2007In: International Journal of Forest Engineering, Vol. 18, p. 9-14Article in journal (Refereed)
  • 26.
    Poom, Leo
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Olsson, Henrik
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Are mechanisms for perception of biological motion different from mechanisms for perception of nonbiological motion?2002In: Perceptual and Motor Skills, ISSN 0031-5125, E-ISSN 1558-688X, Vol. 95, no 3F, p. 1301-1310Article in journal (Refereed)
    Abstract [en]

    We compared the integration of informacion over space and time for perceiving different configurations of moving dots: a walking person (biological motion), rigid three-dimensional shapes, and unidirectional coherent motion of all dots (translation). No performance differences in judging walking direction and coherent translation direction were obtained in conditions with constant presentation times and varying number of target dots (integration over space). Depending on the speed of the two-dimensional configurations judgments were either worse or better than the judgments of walking direction. The results for conditions with different presentation times (integration over time) show that information about biological motion is integrated over time that increases with increasing gait period, while two-dimensional unidirectional motion is integrated over constant time independent of speed. The effect is not due to the oscillatory nature of the biological motion since information about a rigid three-dimensional shape is summed over a constant time independent of the period of the mocion cycle. This could be interpreted as different neural mechanisms mediating the temporal summation for walking direction compared to detecting the orientation of rigid structure, or the direction of two-dimensional unidirectional motion. Since biological motion is characterized by nonrigidity, it is possible that the form itself is integrated over time and not the motion pattern.

  • 27.
    Poom, Leo
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Olsson, Henrik
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Börjesson, Erik
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Dissociations between slant-contrast and reversed slant-contrast2007In: Vision Research, ISSN 0042-6989, E-ISSN 1878-5646, Vol. 47, no 6, p. 746-754Article in journal (Refereed)
    Abstract [en]

    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.

  • 28.
    Van den Berg, Ronald
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Lindskog, Marcus
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Winman, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Recent Is More: A Negative Time-Order Effect in Nonsymbolic Numerical Judgment.2017In: Journal of Experimental Psychology: Human Perception and Performance, ISSN 0096-1523Print, Vol. 43, no 6, p. 1084-1097Article in journal (Refereed)
    Abstract [en]

    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.

  • 29. Wiberg, Henrik
    et al.
    Nilsson, Emma
    Linden, Per
    Svanberg, Bo
    Poom, Leo
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
    Physiological responses related to moderate mental load during car driving in field conditions2015In: Biological Psychology, ISSN 0301-0511, E-ISSN 1873-6246, Vol. 108, p. 115-125Article in journal (Refereed)
    Abstract [en]

    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.

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