Titchener’s ⊥ dissected

Abstract

In three experiments, two independent samples of 12 observers each visually inspected modified versions of Titchener's ⊥ from which the T-junctions had been deleted. For Experiment 1, the ⊥'s two lines had been replaced by dashed lines not meeting in a common point; for Experiment 2, the ⊥ had been reduced to five dots, representing the original lines' end-and midpoints; and for Experiment 3 (in which the second sample of observers served), the ⊥ had been dissected into two separate lines, differently spaced from each other. Observers haptically indicated the lengths of the two orthogonal lines of the modified ⊥s and verbally judged their relative lengths or the distances between the corresponding dots. The common perceptual illusions persisted in Experiments 1 and 2, but were markedly weakened in Experiment 3. Implications for a neurophysiological account of the illusions in terms of bottom-up, long-range interactions between orientation-sensitive mechanisms versus top-down activation of a figural schema are spelled out.

Connectedness underlies the underestimation of the horizontal vertical illusion in L-shaped configurations

“…This explanation also agrees with the claim that within-object comparisons are easier (faster, more accurate) than between-objects comparisons (Behrmann, Zemel, and Mozer, 1998). Moreover, a recent HVI study used dissected T-shape showed that for upright dissected T-shape, the observed HVI strength was still around 10% (Landwehr 2015(Landwehr , pp. 2150.…”

“…The most common way of demonstrating the HVI is perhaps to use the length comparison paradigm, with various line configurations, such as L-shape, inverted T-shape, cross, dissected T-shape, etc. (Avery and Day 1969;Cormack and Cormack 1974;Houck et al 1972;Künnapas 1955Künnapas , 1957Landwehr 2015;Prinzmetal and Gettleman 1993). In addition to the length comparison paradigm, the HVI was also demonstrated by length perception per se, i.e.…”

“…It was thus proposed that the inverted-T illusion consists of two biasesthe vertical bias and the bisection bias. Other types of stimuli configurations, including side-T, cross (Cormack and Cormack 1974;Künnapas 1955) or dissected-T (Landwehr 2015) have also been investigated.…”

Interrelations between the Oppel-Kundt- and the T-illusion

“…The predictions were fulfilled: Relative to what had been observed with dissected ⊥s (Landwehr, 2015), the overestimation of the length of the ⊥'s undivided line was enhanced when this line was dotted, and the other line consisted of two dots only (going from 5.13% to 9.23% for the 3 cm gap, and from 2.23% to 3.88% for the 10 cm gap). Conversely, when the divided line was dotted and the undivided line empty, the ⊥-illusion vanished (going from 2.23% to 0.46% for the 3 cm gap), or, for the 10 cm gap, it even reversed (going from 2.23% to −5.99%).…”

Bimanual thumb-index finger indications of noncorresponding extents

“…And even so, as noticed by a 5-ms sampling rate on a touch-sensitive computer screen, a somewhat arbitrary decision has to be made on what to use as the subject's response (Landwehr, 2014(Landwehr, , p. 1154. Nevertheless, once a set of criteria is consistently applied, reliable data can be obtained (Landwehr, 2015(Landwehr, , 2016.…”