Perceptual interpretation of complex line patterns

Leeuwenberg's coding system for the representation of line pattern interpretations is tentatively applied to the interpretation of complex line patterns, that is, line patterns with intersecting lines. Perceptually preferred interpretations of complex line patterns can only be predicted correctly if two requirements are met: (a) The codes of line patterns should contain information about the objects represented by the line patterns, not about the line patterns as drawings; and (b) effects of the gestalt law of good continuation have to be taken into account.     

Effects of surface markings on judgments of motion direction

The effects of surface markings on perceived motion direction were examined for a rotating sphere in a structure-from-motion display. The markings were dot patterns representing separate line segments or intersecting line segments (crosses) covering the surface of the sphere. The orientation of the surface markings and their intersection angles affected the perceived direction of motion, suggesting that the markings were not interpreted as geodesics or planar cuts on the surface. The perceived direction of motion was biased towards the mean orientation of the markings over the visible area of the surface. A similar bias was observed for translating planar stimuli covered with crosses, suggesting that the bias is not specific to curved surfaces or motion in depth. The deviation between the simulated motion direction and the external horizontal and vertical axes also affected the perceived motion direction. These results suggest that the average orientation of surface contours with respect to an external reference frame influences the perceived direction of motion.     

Simple kinetic information for transparent depth

The present paper reports three investigations of new kinetic information for transparent depth using computer-generated dot patterns. An initial demonstration showed that separation in depth could be obtained by translating rectangular lattices of dots through one another like intersecting columns of marching soldiers. The first two experiments showed that diagonal interactions between lattices created significantly stronger separation than did horizontal or vertical interactions (horizontal was, in turn, stronger than vertical) and that patterns which translated through one another without any of the individual elements intersecting were better separated than those whose rows or columns intersected in register. The third experiment showed that random patterns interacting in any direction created the strongest separations of all the patterns observed. Results were taken to indicate that a unified theory of depth information, developed in the context of James Gibson’s ecological optics, must incorporate both spatial and kinetic structure in its specification of necessary and sufficient stimulus conditions.     

The Poggendorff illusion: Amputations,rotations, and other perturbations

Studies of the Poggendorff illusion (a transversal interrupted by parallel lines) showed that illusory effects increased linearly with increasing separation between the parallels, increased in inverse proportion to the tangent of the angle of intersection between transversal and parallels, decreased whenever line segments (other than a transversal segment) were omitted, decreasing to zero when the segment of a parallel forming the obtuse angle with the transversal was omitted, and varied systematically with the tilt of the whole display, approaching zero when the transversal was oriented in a horizontal or vertical position. Hypothesis: The Poggendorff illusion involves at least three kinds of effects on the perceived orientation of a segment: distortion by other segments (especially a segment intersecting at an obtuse angle), stability of vertical and Horizontal orientations, and assimilation towards vertical or horizontal.     

The effects of stimulus rotation and familiarity in visual search

Rauschenberger and Yantis (2006) observed that an intersecting circle-line combination enjoyed significantly greater search efficiency when it was oriented to resemble a "Q" than when it was oriented so that the intersecting line was vertical (cf. Treisman and Souther, 1985). Although a control experiment made it unlikely that the obliqueness of the line was responsible for the observed benefit, there was no direct evidence that this benefit was attributable to the "Q-ness" of the stimulus. In the present study, a subset of Rauschenberger and Yantis's experiments was repeated with Chinese subjects, who had never been exposed to the Latin alphabet. For these subjects, there was no benefit for the"Q"-like stimulus, in contrast to the results of Rauschenberger and Yantis's study. These results show that a simple 45 degrees rotation of a stimulus can affect search efficiency significantly--but only when this rotation bestows meaning, or familiarity, to that stimulus.     

The perceptual salience of symmetrical and asymmetrical sections of a line

A vertical line segment intersecting a horizontal one at different crossing points generates line sections. Visual perception of such line sections was investigated here in two experiments. In both experiments participants were most accurate and precise when they had to reproduce symmetrical sections. Interestingly, the different asymmetrical sections of a line were not equivalent in terms of participants' performance: constant errors changed as a function of sections and the error curve was nicely interpolated by the composition of two harmonics of the line length. In consistence with the harmonic fitting of the data, we propose that the perceptual salience of specific asymmetrical sections is a byproduct of the automatic triggering of a line midpoint identification process. Being perceptually tuned to symmetry warps our visual representation of the line, which results in systematic misperceptions. The way of bringing present and past experimental findings into a unitary whole is proposed.     

Do McCollough effects provide evidence for global pattern processing?

Contingent color aftereffects (CAEs, or McCollough effects) were induced using two pairs of orthogonally related patterns (horizontal/vertical and concentric/radial) to determine whether the CAEs of the four patterns are independent. Tests using composite test patterns (like those employed by Emerson, Humphrey, & Dodwell, 1985) suggested independent aftereffects. However, tests using unitary patterns indicated additive or competing effects of the four patterns in regions where line orientations were similar, and tests isolating such regions showed clear interactions between the pattern aftereffects. The results fail to support the claim that global (rather than local) features of the patterns control these CAEs.     

Discovery and a Preliminary Study of the Parallel Lines Illusion Change Effect

The parallel lines illusion change effect (discovered by the authors) was studied: When the plane of a parallel-lines illusion figure intersects obliquely with the line of vision and the figure is rotated, using an imaginary perpendicular line between the parallel lines as the axis, the smaller the intersecting angle, the more the illusory effect decreases, until it disappears. If the illusion figure is rotated and any one of the parallel lines is used as the axis, then the smaller the intersecting angle, the greater the illusory effect. The parallel lines illusion change effect may be applicable to the study of geometric-figure illusions.     

The apparent length of a line as a function of its inclination

In the first of two experiments reported here, subjects adjusted the length of a variable line until it appeared to be as long as a standard line. There were two sizes of standard line, 3 and 6 inches, and each was shown vertically for some trials and horizontally for others. The variable line was presented in each of the 10° positions from 0° (horizontal), through 90° (vertical), to 170°. The principal results of the first experiment are:

(1) Vertical lines look longer than horizontal lines of the same length, but lines tilted 20°-30° to the left of vertical look longer than lines in any other orientation. The results are asymmetrical, because lines tilted to the right of vertical do not look as long as those tilted to the left of vertical.

(2) The variability of the settings increases as the angle increases between the standard and variable lines.

(3) When they are expressed in percentage terms, the data obtained with the 3-and 6-inch standards are virtually identical, i.e. the data for the 3-inch standard can be made to match those for the 6-inch standard simply by doubling the former.

(4) There are enormous differences among subjects in the patterns of settings made at the various angles. A few subjects apparently experienced no illusory effects since they adjusted the variable line to about the same physical length irrespective of its orientation. Other subjects showed exaggerated overestimations of the variable line for vertical and near-vertical positions.

In the first experiment, the variable line was always to the left of the standard, and it was natural to assume that this position effect had somehow produced the asymmetry noted in paragraph 1 above. This hypothesis was tested in the second experiment which alternatively showed the variable line above, below, to the right of, and to the left of the standard line. The results of this experiment generally confirm the data of the first experiment in showing that lines tilted 20°-30° to the left of vertical look longer than lines tilted to any other position. In addition, the second experiment shows that this asymmetry in the results is not a function of the relative positions of the variable and standard lines. In general, however, overestimations of length are smaller when the two lines are one above the other, greater when the two lines are side by side.     

Integration of local features as a function of global goodness and spacing

In two experiments, the accuracy with which subjects detected a conjunction of features was examined as a function of the spacing between items and the goodness of the axis along which they were located. In each array, two items were arranged along a vertical, a horizontal, or a diagonal axis. Based on the well-established oblique effect, the vertical and horizontal axes were considered to be good global patterns and the diagonals were considered to be poor. In Experiment 1, the two items in an array could be two horizontal lines, two vertical lines, a vertical and a horizontal line, or a plus sign with one of the single lines. In Experiment 2, a positive- and a negative-diagonal line were used as the individual features, and an "X" was used as the conjunction. The results from Experiment 1 indicated that global goodness influenced only the rate of illusory conjunctions, and not of feature errors. Illusory conjunctions of vertical and horizontal line segments were more likely to occur in vertical and horizontal arrangements. The results from Experiment 2 revealed a reversal of the effect of global goodness on the rate of illusory conjunctions: Illusory conjunctions of negative- and positive-diagonal line segments were more likely to occur in diagonal arrangements. The results of both experiments taken together showed the existence of an important and new factor that influences the likelihood that features of shape will be conjoined: the ease with which line segments conjoin when they are translated along their extent toward each other. In both experiments, greater spacing between items produced more feature-identification errors and fewer feature-integration errors than did less spacing.     

Three elemental illusions determine the Zöllner illusion

We have discovered an apparent contraction illusion of acute angles in a special form of the Z?llner figure at the intersecting angles between 36 degrees and 83 degrees (i.e., a reversal of the Z?llner illusion). The necessary condition for this illusion is that inducing lines are long enough and the induced line (test line) is single. When an illusory line is used as the induced line, the magnitude of contraction increases. Short inducing lines give no illusion or a slight expansion of acute angles at the intersecting angle of 45 degrees. We have ascertained that the source of this expansion is the narrow region in the vicinity of the induced line, whereas the source of the contraction is much broader regions. Furthermore, we have discovered another expansion mechanism, which is generated by the symmetrical configuration of the standard Z?llner figure.     

What’s up in mental rotation?

We report two experiments on the influence of head tilt on mental rotation. In Experiment I, subjects decided whether dot patterns were or were not repeated about a line. Their reaction times (RTs) were consistent with the interpretation that they mentally rotated the patterns so that the line was subjectively vertical before making their decisions. When the subjects tilted their heads, the RT functions shifted in the direction of the tilt, indicating that the subjective vertical lay closer to the retinal than to the gravitational vertical. In Experiment II, subjects decided whether singly presented alphanumeric characters in various orientations were standard or backward (mirror-reversed). Again, analysis of their RTs suggested mental rotation to the standard upright, but the function was unaffected by head tilt; in this case, the subjects operated in subjective gravitational rather than retinal coordinates. The choice of retinal or gravitational coordinates may depend on whether the stimuli are interpreted egocentrically or as part of the external world.     

Detection of symmetry as a function of angular orientation.

Subjects decided as quickly as possible whether dot patterns were or were not symmetrical about a line. Their decision times were shorter when the line was verticle and increased as the angle between the line and the verticle increased. This orientation function was essentially the same whether or not the subjects knew in advance what the orientation of the line would be. When the subjects tilted their heads, the function shifted in the direction of the head tilt, indicating that it was tied more closely to retinal than to gravitational coordinates. These data can be interpreted to mean that people mentally rotate patterns to a vertical orientation before judging their symmetry. This in turn suggests that the "template" for detecting symmetry may itself be embedded symmetrically in the brain.     

Discrimination of structure: II. Feature binding

In 3 experiments, pigeons acquired a discrimination between patterns comprising the same features. Thus vertical green bars beside horizontal red bars might have signaled food, and horizontal green bars beside vertical red bars might have signaled no food. The solution of this discrimination can be explained by assuming each pattern is represented either by a template or by structural features that are sensitive to combinations of color and line orientation. The 1st explanation predicts subjects should react to a training pattern rotated 90 degrees in the same way as the pattern on which it is based. The 2nd explanation predicts these patterns should be treated as if they signal opposing outcomes. The experiments confirmed the 2nd of these predictions.     

Lateral biases and reading direction: a dissociation between aesthetic preference and line bisection

Perceptual asymmetries for tasks involving aesthetic preference or line bisection can be affected by asymmetrical neurological mechanisms or left/right reading habits. This study investigated the relative contribution of these mechanisms in 100 readers of Japanese and English. Participants made aesthetic judgments between pairs of mirror-reversed pictures showing: (a) static objects, (b) moving objects and (c) landscapes. A line bisection task was also administered. There was a strong effect of reading direction for static and mobile objects whereby Japanese readers preferred objects with a right-to-left directionality (and vice versa for English readers). In contrast, similar patterns were observed for the Japanese and English readers for the landscape and line bisection tasks. The results show that reading habits affect aesthetic judgments for static and moving object tasks, but not the landscape and line bisection tasks. The difference between the tasks may be related to the horizontal/vertical geometry of the stimuli, which makes the landscape and line bisection tasks more prone to universal effects related to cerebral dominance.     

Figure embeddedness depends on contour orientation

The “oblique effect” was studied using an embedded figures task in which complex patterns and hidden forms were rotated into different orientations. One set of stimuli (Series I) used patterns consisting either entirely of depending on rotation) horizontal and vertical line segments or entirely of obliques. A second set of stimuli (Series II) used patterns composed of horizontal, vertical, and oblique segments in equal proportions. With Series I, both form and complex pattern orientations changed with rotation. In Series II, rotation changed the orientation of the hidden forms, but not the relative proportion of contour orientations in the complex patterns. Significantly longer search times were required to find forms embedded within the obliquely oriented patterns of Series I. There were no significant differences in Series II. These results are discussed in terms of the role contextual contours may play in the detection of differently oriented form.     

Hemispheric differences in visual search of simple line arrays

Summary The effects of perceptual organization on hemispheric visual-information processing were assessed with stimulus arrays composed of short lines arranged in columns. A visual-search task was employed in which subjects judged whether all the lines were vertical (same) or whether a single horizontal line was present (different). Stimulus-display organization was manipulated in two experiments by variation of line density, linear organization, and array size. In general, left-visual-field/right-hemisphere presentations demonstrated more rapid and accurate responses when the display was perceived as a whole. Right-visual-field/left-hemisphere superiorities were observed when the display organization coerced assessment of individual array elements because the physical qualities of the stimulus did not effect a gestalt whole. Response times increased somewhat with increases in array size, although these effects interacted with other stimulus variables. Error rates tended to follow the reaction-time patterns. The results suggest that laterality differences in visual search are governed by stimulus properties which contribute to, or inhibit, the perception of a display as a gestalt. The implications of these findings for theoretical interpretations of hemispheric specialization are discussed.     

Three elemental illusions determine theZöllner illusion

We have discovered an apparent contraction illusion of acute angles in a special form of the Zöllner figure at the intersecting angles between 36° and 83° (i.e., a reversal of the Zöllner illusion). The necessary condition for this illusion is that inducing lines are long enough and the induced Une (test line) is single. When an illusory line is usedas the induced line, the magnitude of contraction increases. Short inducing lines give no illusion or a slight expansion of acute angles at the intersecting angle of 45°. We have ascertained that the source of this expansion is the narrow region in the vicinity of the induced line, whereas the source of the contraction is much broader regions. Furthermore, we have discovered another expansion mechanism, which is generated by the symmetrical configuration of the standard Zöllner figure.     

The role of structural components in the Mueller-Lyer illusion

In order to assess the role of the structural components of the Mueller-Lyer illusion, subjects reproduced the central extent of standard Mueller-Lyer figures and configural variations. Illusory magnitude of the underestimated wings-in and overestimated wings-out figures was examined with selective amputations of the oblique wings and central line segment (shaft). Variations were presented at 0, 45, 90, and 135 deg from vertical. Orientation had no reliable effect on illusory magnitude. Elimination of the shaft effected a decrease in the apparent extent for all variations, presumably due to the addition of the filled-unfilled space illusory effect to the standard Mueller-Lyer effect. A second study corroborated this finding The decrease in apparent extent consequent to shaft removal occurred independently of any response factor. Selective wing removal differentially decreased the illusory magnitude of the standard Mueller-Lyer figures; this was discussed with regard to a dual-illusion hypothesis. Finally, variations that contained no intersecting lines produced a significant illusion in the direction of the standard Mueller-Lyer figures, suggesting the involvement of higher level, nonperipheral distortion mechanisms.     

The joint

Some concave volumes are perceived as compositions of joined objects. Joined objects are optically undetermined, being compatible with three possible solutions: an empty intersection volume bounded by two indented objects; an intersection volume entirely filled-in by parts of two indented objects; a totally convex object joined to an indented object (the solution preferred by most perceivers). Knowledge of material penetrability does not predict 3D amodal completion. To identify relevant factors we selected different compositions and ran a multiple-regression analysis of completion choices. After eliminating colour, we considered six spatial factors: relative position along the vertical, relative size, orientation, proximity to the observer, minimization of completed parts, support relationship. The first two factors played a major role. The comparison of choices by upright versus inverted observers indicated that relative position along the vertical depends more on gravitational than egocentric coordinates. In conclusion, when relative spatial position and relative size cooperate, amodal completion of intersecting solids generates strong effects, which can overcome logical expectations.