The effects of angle-arm length on judgments of angle magnitude and orientation contrast

Abstract

Acute angles frequently are overestimated, an effect that has been attributed to lateral inhibitory mechanisms. It can be derived from such theories that lengthening the arms of an angle should either reduce or not affect its judged subtense. However, in Experiments 1 and 2, it was found that angles with longer arms were judged larger. In Experiment 3, direct measures of anglearm orientation indicated that orientation contrast does not increase with angle-arm length, that it decreases with distance from the angle vertex, and that these effects are not averaged along the entire length of the arm. It follows that inhibitory mechanisms alone cannot explain why longer armed angles appear larger or why angle arms appear straight rather than bowed. It is suggested that a distinction is required between the orientation and the angular domains and that the latter judgments depend, at least partially, on the space or area within an angle. The fact that angles appear unbowed may reflect the fact that perceived orientation differences occur along an angle's arm only when matches are made to small segments of the arm.

Orientation specificity of length assimilation and contrast

“…Finally, Experiment 4 demonstrated that the sequential length contrast (length aftereffect) produced by a 5-sec prior inspection of a contextual line was independent of orientation, whereas the contrast produced by 60 sec of contextual-line inspection showed some degree of orientation specificity. These results, combined with those obtained with orientation illusions (Tyler & Nakayama, 1984;Wenderoth & Johnson, 1984;Wenderoth, O'Connor, & Johnson, 1986), suggest a qualitative relationship of length and orientation coding that is characterized by partial and mutual overlap of length and orientation information.The parallel-lines array is a minimal configuration for producing an illusion of perceived length. The direction of this distortion of perceived length depends on the spatial and temporal relationship of the test line and a parallel contextual line.…”

“…Rreferring to the analysis described in Figure 1, the results of Tyler and Nakayama (1984) and Wenderoth et al (1986) rule out relationship A. Additionally, the results of Wenderoth and Johnson (1984) rule out relationships B and C. Finally, the results of these first two experiments rule out relationship D, since the obtained length distortions seemed independent of orientation. Thus, within the attentive field, length and orientation coding seem to partially and mutually overlap (relationship E).…”

“…Relationship E (partial overlap of length and orientation information) is a good description of this relationship. The relationship implies at least three kinds of psychophysical effects, all of which have now been demonstrated-a length distortion independent of orientation, an orientation distortion independent of length (Wenderoth & Johnson, 1984), and a length-dependent orientation distortion (Tyler & Nakayama, 1984;Wenderoth et al, 1986). The demonstration of the orientationcontingent length distortion (Experiment 4, 6O-sec condition) completed the set of effects implied by relationship E.…”

“…The entire procedure required approximately 16 min for each of the 18 observers in the 5-sec condition, and 42 min for each of the 18 observers in the 6O-sec condition. possible psychophysical effects that can be derived from this relationship has now been demonstrated: a lengthcontingent orientation distortion (Tyler & Nakayama, 1984;Wenderoth et al, 1986), a non-length-contingent orientation distortion (Wenderoth & Johnson, 1984), an orientation-contingent length distortion (Experiment 4, 6O-sec condition), and a non-orientation-eontingent length distortion (Experiments 1 and 2 combined, Experiment 3, and Experiment 4, 5-sec condition).…”

“…Thus, rela-LENGTH ASSIMILATION AND CONTRAST 447 tionship A is not a correct description of length and orientation coding within the visual system. Additionally, Wenderoth and Johnson (1984) reported that the magnitude of the tilt illusion was not changed when the length of both the contextual and test arms forming an angle varied. This result indicates at least a partial independence of orientation and length coding, and thus rules out relationships B (redundancy of coding) and C (orientation coding as a subset of length coding).…”