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Biomedical subjects

P Wenderoth

Publications and source records attributed to P Wenderoth.

At least 73 records · Page 4Linked to original sources
PubMed1985

What is the appropriate control for the tilt illusion?

Recently it has been suggested that when tilt illusions are measured by parallel matching to the test arm of an acute angle, the usual control condition involving a match to the test arm in the absence of the inducing arm is inappropriate. According to Hotopf et al this is so because the pretest contains a second, depth-based illusory effect which is not contained in the test conditions. Whereas Hotopf et al gave indirect evidence for this claim, direct evidence is presented here for their assertion. The results suggest that there is no single stimulus configuration which could serve as a pretest control for all tilt illusion stimuli. Rather, the condition in which the test and inducing lines intersect at 90 degrees probably is the appropriate control for all other inducing-test-line angle displays.

Depth Perception↗
PubMed1981

Are the obtuse angles the key components of the Poggendorff illusion?

An experiment is reported which confirms and extends a previous finding that amputations of the Poggendorff figure do not necessarily result in large positive effects with obtuse-angle stimuli, and small or even negative effects with acute-angle stimuli. Indeed, the acute-angle effects found were significantly greater than the obtuse-angle effects, and the full Poggendorff error was not explicable in terms of the linear summation of the component-angle effects. An 'alignment displacement effect' reported earlier by Hotopf and Obonai was shown to occur, but could not be an important component of the Poggendorff illusion.

Adolescent↗
PubMed1981

The role of the second oblique in the Poggendorff illusion.

It has been observed previously in the classic Poggendorff illusion figure that the end of the oblique line which abuts onto the vertical parallel appears more misaligned than its free end. Various theories suggest that angular distortions are largest at the point of abutment. Two experiments are reported which, however, suggest that, compared to displays in which a single dot is aligned with an oblique line, the introduction of a second, parallel oblique segment does not increase errors more at the abutting tip than at the free end, but, rather, reduces them more at the free end. These results not only cast doubt on the relative importance of angular effects alone in the classic Poggendorff display, but also emphasise the complexity of that figure as a tool in the investigation of visual processing.

Humans↗
PubMed1979

A comparison of visual tilt illusions measured by the techniques of verticle setting, parallel matching, and dot alignment.

The tilt illusion (TI) was investigated by using both short (19 min) and long (2 deg 6 min) test lines, at three angles of test line-inducing line separation (15 degrees, 45 degrees, and 75 degrees). Three groups of ten observers each provided data under one of three task conditions: vertical judgment, parallel matching, and dot alignment on a common visual display. The main result was that both the vertical judgment and the parallel matching task provided similar, classic TI angular functions with the means ordered 15 degrees greater than 45 degrees greater than 75 degrees and with small attraction effects at 75 degrees in three of the four relevant functions. The third task, dot alignment, yielded results different from the average of the other two: no attraction effects occurred and, with the short test line, the obtained mean illusion at 45 degrees exceeded those at the other intersect angles. These results are consistent with alignment data reported by others. One explanation is that the inducing line produces an apparent bowing of the test line which would be reflected in dot alignments but not in vertical setting or in parallel matching. However, direct evidence does not support this hypothesis. An alternate hypothesis, for which independent evidence exists, is that alignment errors reflect perceptual mistracking but that the origin of these errors is not the tip of the test line but within it. Although this does not explain dot alignment errors, it highlights their complexity and the need to interpret them with caution.

Form Perception↗
PubMed1979

Angle-matching illusions and perceived line orientation.

Spatial illusions which occur in angle-matching tasks were examined in six experiments using two different kinds of display. In experiments 1 and 2 illusory errors generally were in the direction predicted by Lennie's hypothesis which states that angle arms are attracted perceptually towards the oblique axes of space, although the display used in these experiments differed from Lennie's. However, experiment 3 showed that these errors might equally be explained by the addition of interactive effects between angle arms (tilt illusions). Parametric investigation of Lennie's figures (experiments 4 and 5) showed that thelargest angular illusion occurred with the largest angle used (45 degrees) and an intermediate line length (2 deg 7 min). These angular illusions were not explicable by the addition of tilt illusions (experiment 6), suggesting that different judgmental processes may underlie orientation and angle estimation.

Discrimination Learning↗