Influence of a stereo surface on the perceived tilt of a monocular line.

This study addressed the issue of how a stereo-specified surface influences the perceived two-dimensional orientation of a monocularly viewed line. In a series of three experiments, it was found that, in general, when a monocular line was embedded in a disparity field specifying a planar surface slanted about the horizontal axis, the tilt of the line depended on the slant of the surface in which it was embedded and on whether the line was presented in the left or in the right visual field. These results, predicted by perspective geometry, are compatible with the hypothesis that the monocular line is perceived as part of the stereo surface. Moreover, it was found that timing is a crucial factor in determining the strength of the effect. The effect was at a maximum when the monocular line and the stereo surface were presented together, with no prior presentation of the surface. The influence of the stereo surface on the monocular line was substantially reduced, however, when the surface alone preceded the combined presentation of the line and the surface.     

Effects of partial occlusion on perceived surface segregation

Tests are reported of the possibility that local information from contour junctions and from corners of intersecting surfaces is used for perceived surface segregation. Stimuli were two intersecting squares with small disks occluding different parts of the squares. The perceived segregation of the squares from one another decreased as the amount of occlusion of parts of the squares increased. This segregation was less when disks occluded parts of contours than when disks occluded parts entirely inside the squares. Occlusion of parts of contours reduced segregation independently of whether contour junctions or corners were visible or invisible, both where the intersecting surfaces were transparent squares and when they were outlined squares. The present findings show that local information from contour junctions or from corners is not used for surface segregation, and confirm that this segregation is determined by global processes of grouping of areas and of extrapolation of contours.     

Influence of flicker on perceived size and depth

Previous research (e.g., Wong & Weisstein, 1984a, 1985) has shown that flickering stimuli appear to be more distant than nonflickering stimuli at the same physical distance. Given this relation between flicker and perceived depth, inappropriate constancy scaling theories predict that flickering stimuli should be perceived as larger than nonflickering ones. In contrast, links between flicker and motion perception suggest that flickering stimuli should be perceived as smaller than nonflickering ones. Two experiments tested these contrasting predictions. In Experiment 1, 22 subjects compared flickering and nonflickering vertical lines and reported that the flickering stimulus appeared significantly smaller than the nonflickering one. In Experiment 2, 21 subjects reported that the stimuli used in Experiment 1 produced depth effects similar to those reported in previous experiments: flickering stimuli were perceived as more distant than nonflickering ones. The observed effect of flicker on perceived size was contrary to predictions from inappropriate constancy scaling theory, but consistent with views that motion and flicker are processed by the same pathway.     

The effect of line configuration on perceived numerosity of dotted lines

Estimates of the number of objects in a line are made in many different situations. This paper demonstrates that besides the actual number of dots, aspects of line configuration affect the perceived numerosity of dotted lines. Experiment 1 provides evidence that the highly studied “clutter effect” in distance perception research replicates to the numerosity domain so that lines made up of more segments are perceived to contain more dots. Experiments 2–5 provide nomological validity for the recently proposed “direct distance” effect in distance perceptions by showing that numerosity perceptions are higher the greater the euclidean length between the line end points and by manipulating euclidean length in three orthogonal ways: the relative length of segments (Experiment 2), the angle between segments (Experiment 3), and the general direction of segments (Experiment 4). Experiment 5 conceptually replicates the results of Experiments 2–4 utilizing stimuli-based versus memory-based judgments and a discrimination task. Experiments 6 and 7 extend the research on spatial perception by demonstrating that the use of euclidean length as a source of information is inversely related to line width, with width varied through clutter (Experiment 6) and total line length (Experiment 7). Overall, the results demonstrate that the robustness of the euclidean length effect is contingent on the salience of alternative spatial heuristics-specifically, euclidean width. Theoretical implications are discussed.     

The influence of object size and surface shape on shape constancy from stereo

The failure of shape constancy from stereoscopic information is widely reported in the literature. In this study we investigate how shape constancy is influenced by the size of the object and by the shape of the object's surface. Participants performed a shape-judgment task on objects of five sizes with three different surface shapes. The shapes used were: a frontoparallel rectangle, a triangular ridge surface, and a cylindrical surface, all of which contained the same maximum depth information, but different variations in depth across the surface. The results showed that, generally, small objects appear stretched and large objects appear squashed along the depth dimension. We also found a larger variance in shape judgments for rectangular stimuli than for cylindrical and ridge-shaped stimuli, suggesting that, when performing shape judgments with cylindrical and ridge-shaped stimuli, observers rely on a higher-order shape representation.     

Influence of acetaminophen consumption on perceived exertion at the lactate concentration threshold

The purpose of this investigation was to study effects of acetaminophen consumption on ratings of perceived exertion and estimated time limit responses at the lactate threshold. 98 young regional to national level athletes performed a graded exhausting exercise on an outdoor running track to estimate their maximal aerobic velocity and the velocity associated with their lactate concentration threshold. Urine (30 mL) was collected during this test and analysed for numerous substances. During urinary screening for doping substances, 9 acetaminophen consumers (9.2%) among the 98 included athletes were detected. These acetaminophen consumers have significantly lower perceived exertion at velocity corresponding to the lactate concentration threshold than nonconsumers (11.9 +/- 2.1 vs 13.6 +/- 2.1, respectively) although they were at the same relative exercise intensity. This result shows that acetaminophen consumption may have mediated the perceived exertion response at the lactate concentration threshold. This may then suggest that the pain induced by training load could be a factor in use of self-prescribed pain relievers. Such consumption must be taken into account by medical staff, trainers, or educators who have to give information on the use and adverse effects of this substance and to propose palliative methods to their athletes.     

Test of Petter's rule for perceived surface stratification

Petter's rule applies to two-dimensional patterns formed by two overlapping surfaces that alternatively appear in front of one another. It states that the surface with the shorter contours in the region where the surfaces look superimposed has a greater probability of appearing in front of the other surface. An experiment is reported the results of which show that Petter's rule is valid for chromatically homogeneous and for uniformly dense dotted patterns, and invalid for different kinds of chromatically inhomogeneous patterns. Petter's rule has been found to be valid when the overlapping surfaces have contours with gaps. It is proposed that Petter's rule derives from the dynamics of filling-in of contour gaps.     

Expanding on the mental number line: Zero is perceived as the "smallest"

The representation of 0 in healthy adults was studied with the physical comparison task. Automatic processing of numbers, as indicated by the size congruity effect, was used for detecting the basic numerical representations stored in long-term memory. The size congruity effect usually increases with numerical distance between the physically compared numbers. This increase was attenuated for comparisons to 0 or 1 (but not to 2) when they were perceived as the smallest number in the set. Furthermore, the size congruity effect was enlarged in these cases. These results indicate an end effect in automatic processing of numbers and suggest that 0, or 1 in the absence of 0, is perceived as the smallest entity on the mental number line. The implications of these findings are discussed with regard to models of number representation. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

The tilt illusion: Length and luminance changes of induction line and third (disinhibiting) line

Direct effects (acute-angle expansion) and indirect effects (acute angle contraction) aspects of the tilt illusion were reduced by reductions in the length as well as the luminance of the induction line, and also by the addition of a third line to the display. When this third (disinhibiting) line was also reduced in length and luminance, the reduction in the illusion became less and the illusion increased in magnitude. The illusion size was also changed by increasing the orientation difference between the disinhibiting line and the induction line. It is argued that these effects are mediated by (lateral) inhibition and disinhibition between mechanisms responsible for orientation coding in the visual system.     

Influence of emotional content and perceived relevance on spread of urban legends: a pilot study

This study examined factors thought to be associated with the spread of urban legends. 62 participants (84% female, 65% white, M age = 22 yr.) read 15 urban legends, 3 of which had a stated local component, and rated various characteristics of each legend, including how scary it was, how believable it was, and how likely the participants would be to tell it to someone else. As predicted, both a high fear rating and a high believability rating were positively correlated with the reported intent to tell (rho60 = .41, p < .0001 and rho60 = .67, p < .02, respectively). There was also a significant positive correlation between familiarity and intent to tell (rho60 = .22, p < .0001); however, presence of a local connection was not strongly correlated with intent to tell. It is possible that the local stories were less believable because they all involved ghosts.     

Integration of stereo and texture cues in the formation of discontinuities during three-dimensional surface interpolation

A series of stereograms are presented which demonstrate that texture boundaries can strongly influence the perception of discontinuities between neighbouring three-dimensional (3-D) surfaces portrayed by means of stereo cues. In these demonstration figures, no stereo information is available in the immediate vicinity of the boundary between the two 3-D stereo surfaces because all texture in that region is removed in one eye's view. On the other hand, various forms of texture boundary information are provided in the resulting monocular region. This stimulus paradigm is used to explore the question: what influence does texture boundary information have on the nature of the perceived 3-D surface that is interpolated between two stimulus regions which carry stereo cues? It is shown that if a clear-cut texture boundary is present in the monocular region then this is used by the human visual system to fix the perceived location of 3-D crease and step surface discontinuities between the stereo regions. Collett (1985) explored this issue with a similar methodology and reported weak and unreliable assistance from monocular texture boundaries in helping shape 3-D stereo surface discontinuities. The strong and robust phenomena demonstrated here seem to rely on two main differences between the present stimuli and those of Collett. In the present stimuli, figurally continuous textures containing strong texture boundaries are used, together with a technique for minimising the complications, including binocular rivalry, that arise from the borders of the stimulus regions present in only one half of each stereogram.     

Influence of hue,value, and chroma on the perceived heaviness of colors

In addition to its information content, color iz known to have certain affective qualities. We have investigated the assertion that colors have different apparent weights using a magnitude estimation technique. We find that the apparent heaviness of colors is an increasing function of ehroma or saturation and a decreasing function of value or lightness. Hue has little influence on the apparent weight of color.     

Influence of drafting during swimming on ratings of perceived exertion during a swim-to-cycle transition in well-trained triathletes

After the swim to cycle transition of a triathlon, perceived exertion (RPE) during cycling was higher than during a single cycling bout for 8 well-trained triathletes, but swimming in a drafting position led to lower RPE responses and energy cost of cycling than swimming alone.     

Determinants of perceived surface transparency in two-dimensional achromatic textured patterns

Achromatic transparency in 2-D surfaces composed of three adjacent areas, one created from the others, occurs when in the created area it is possible to see the two colours of the adjacent areas. Displays with two white and black intersecting bars were produced to verify the possibility of perceiving transparency in the intersection area when this was subdivided into a different number of white and black diamonds. By increasing the spatial frequency of the elements in the intersection area we investigated the impression of transparency, and found that (i) the impression of transparency increases up to a spatial frequency of 10 cycles deg(-1) and then levels off, (ii) there is a transition from a perception of transparency in which white and black are well discriminable to a perception in which a perceptually uniform grey is seen, (iii) the perception of transparency occurring when colours are discriminated seems consistent with Helson's area-luminance hypothesis [1964, in Adaptation Level Theory (New York: Harper & Row) pp 282-292], according to which the increase of spatial frequency determines the transition from the phenomenon of contrast to that of assimilation.     

Effect of planar cuts’ orientation on the perceived surface layout and object’s shape

The effect of the orientation of the cutting planes producing planar curves over the surface of an object on its perceived pose and shape was investigated for line drawings representing three-dimensional objects. The results suggest that the orientational flow produced by the surface curves introduces an apparent object rotation in depth and in the image plane and changes in its perceived elongation. The apparent location of the nearest points is determined by the points of maximal view-dependent unsigned curvature of the surface curves. The data are discussed in relation to the interaction of the shape-from-silhouette system and shape-from-contour system and its effect on the interpretation of the surface contours with respect to the surface geometry.     

The effect of perceived distance on perceived movement

Equations were developed to predict the apparent motion of a physically stationary object resulting from head movement as a function of errors in the perceived distances of the object or of its parts. These equations, which specify the apparent motion in terms of relative and common components, were applied to the results of two experiments. In the experiments, the perceived slant of an object was varied with respect to its physical slant by means of perspective cues. In Experiment I, O reported the apparent motion and apparent distance of each end of the object independently. The results are consistent with the equations in terms of apparent relative motion, but not in terms of apparent common motion. The latter results are attributed to the tendency for apparent relative motion to dominate apparent common motion when both are present simultaneously. In Experiment II, a direct report of apparent relative motion (in this case, apparent rotation) was obtained for illusory slants of a physically frontoparallel object. It was found that apparent rotations in the predicted direction occurred as a result of head motion, even though under these conditions no rotary motion was present on the retina.