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Leo Poom

Publications and source records attributed to Leo Poom.

8 recordsLinked to original sources
PubMed2006

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.

Adult↗
PubMed2005

Visual memory needs categories.

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.

Adult↗
PubMed2005

Colour, polarity, disparity, and texture contributions to motion segregation.

We measured how different cues are combined in motion-segregation processes by using motion stimuli where randomly distributed target dots were organised in global revolving motion while the remaining noise dots performed random motion. Target dots were cued with a different colour, polarity, disparity depth, or texture orientation than the noise dots, or they were the same as the noise dots. The stimuli were presented with a prolonged static cue preview which provided position cues to target dots or, briefly with static pre-target and post-target noise frames, which provided false position cues (no preview). All cues efficiently facilitated global motion segregation in cued-preview conditions. Colour completely failed to facilitate global motion segregation in no-preview conditions. Polarity and disparity facilitated segregation in no-preview conditions, although sensitivities were lower than in the preview conditions. Remarkably, texture orientation largely facilitated motion segregation by the same amount in both cued-preview and no-preview conditions. So, colour provides only position cues to the motion-segregation task whereas texture orientation, disparity, and to a lesser extent polarity are integrated with the segregation process.

Color Perception↗
PubMed2004

Good continuation with kinetic edges.

We examined the perceptual formation of extended contours from second-order kinetic-edges created by motion discontinuities. Paths were formed by spatially separate kinetic-edge elements, aligned along smooth paths, and embedded in randomly oriented noise elements. Path detection was severely degraded when the sign of motion contrast alternated along the path compared to when the same sign was used, or if random motion direction was assigned to each edge element, or if alternating opposite motion directions was used along the paths. Performance increased monotonically with the length of the path. Irrespectively of path curvature a fast temporal summation occurs within the first 200-400 ms and then levels off. Hence, the kinetic-edge grouping is relatively fast and a pure second-order process that senses whether the motion is globally in the same phase and direction along extended contours.

Form Perception↗
PubMed2002

Visual binding of luminance, motion and disparity edges.

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.

Humans↗
PubMed2002

Seeing stereoscopic depth from disparity between kinetic edges.

Traditionally, it is assumed that stereovision operates only on the positional difference (disparity) between luminance-defined features in the images in the left and the right eye. Here, I show that stereoscopic depth can be seen from disparity between edges created by relative motion of texture elements, and between edges created by correlated flicker of stationary texture elements. Luminance-based stereopsis was impossible since the texture was binocularly uncorrelated. Positional disparity of the centre of revolving patterns was not an efficient depth cue. Stereopsis from the stimuli presented here was possible even without binocular overlap of textured areas. The results provide evidence that positional disparity of kinetic edges, defined by correlated flicker or motion contrast alone, can be used as matching features to recover stereoscopic depth.

Cues↗
PubMed2002

Are mechanisms for perception of biological motion different from mechanisms for perception of nonbiological motion?

We compared the integration of information 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 motion 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.

Algorithms↗