Search PubMed⌕ Search

Biomedical subjects

W H Hotopf

Publications and source records attributed to W H Hotopf.

11 recordsLinked to original sources
PubMed1993

How the range effect contaminates control scores in studies of visual illusions.

The relationship between mean control scores and mean experimental scores in 23 experiments on alignment illusions has been examined. Evidence is presented to show that, through the operation of the range effect, control scores are biased to a significant degree in the direction of experimental scores. The implications of this are considered, not only as regards the value of control scores in psychophysical studies, but also as further evidence of the dangers of within-subjects experimental designs when issues depend upon the values of extreme points in a range of values.

Attention↗
PubMed1990

How far can attraction-caused misalignment account for the Morinaga misalignment effect?

When a line (the pointer) is collinear with a dot, the addition of a second line (the induction line) contiguous with the dot or near it may cause the pointer to appear to be collinear with a point further along or nearer to the induction line. The geometrical relations upon which this effect (which we call attraction-caused misalignment) depends, have been studied with the Obonai and Wundt-Loeb (Hotopf, 1981; Hotopf & Brown, 1988) figures. Drawing upon the studies of misalignment in the Morinaga figure carried out by Restle (1976), Day, Bellamy, and Norman (1983), and Day and Kasperczyk (1985), as well as upon two new experiments, we show that misalignment in the Morinaga figure is also attraction-caused misalignment, as previously defined. We conclude with a discussion of a number of theories that aim at accounting for attraction misalignment.

Adult↗
PubMed1989

Perceived diagonals in grids and lattices.

Diagonal lines are seen running between the intersections in repetitive grid patterns, but not in lattices of dots. We show that these lines, which are of reverse contrast to the grid, cannot be explained by global Fourier components in the pattern, or by low-pass orientation-specific filtering. The lines depend upon local diagonal components at the intersection, and we suggest that the output of local detectors are combined by collector units receiving their input from different visual field positions. Relevant neurophysiological evidence is discussed, and the model is extended to subjective contours and the Fraser twisted cord.

Form Perception↗
PubMed1988

Constant errors in judgements of collinearity due to the presence of neighbouring objects.

If a line (the pointer) is aligned with a dot (the target) that stands on another line (the induction line) which is at an angle to the pointer, the pointer and the dot may no longer appear collinear. Whether they do or not depends upon the angle formed by the pointer with the induction line: the smaller the angle, the greater the misalignment effect. Misalignment is always in the direction of the induction line, which is why this alignment illusion is called attraction-caused misalignment (attraction misalignment for short). Three experiments are described in which this illusion is explored further. In the first it is shown that the induction line can exert its influence even when not contiguous with the target, though the size of the effect varies inversely with the distance of the induction line from the target. In the second experiment it is demonstrated that a dot as well as a line can induce attraction misalignment and that similarity between the induction and target items increases misalignment. Evidence in support of the theory that the termination of the induction line, as well as the part contiguous with the target dot, may induce attraction misalignment is provided in the third experiment.

Adult↗
PubMed1985

Eye movements and illusions of alignment.

Extraction of the location of a target in the visual periphery is a fundamental visual process which may be manifested both in conscious judgments of location, such as decisions about alignment, and in the processing required to execute an eye movement to a peripheral target. In both cases, location judgement is affected by the neighbouring visual configuration. An experiment is reported in which the amplitude of saccadic eye movements has been measured to study the effect of a configuration consisting of a single 'induction line'. The results demonstrate systematic effects of this line on the size of the saccade which are closely similar to those previously found in an alignment task.

Eye Movements↗
PubMed1983

Position in the visual field and spatial expansion.

Measurements of the tilt illusion by parallelism matches have taken as their baseline data estimates of parallelism between two lines. This is because Carpenter and Blakemore and others found in this situation that parallel lines appeared to diverge at their upper ends. It was hypothesised that this effect was due to inappropriate constancy scaling-the parallel lines being interpreted as being located in a receding plane-and that consequently it was inappropriate to take this effect into account in assessing the degree of the tilt illusion. To test the theory, a horizontal line was compared with other horizontal and vertical lines lower down in the visual field. A tendency to underestimate the length of lines lower down in the visual field was found but this varied inversely with distance from the standard. The findings were accounted for on the assumption that the occurrence of inappropriate constancy scaling depended upon prior organization by contiguity which determined whether the two lines were taken as a group or not.

Discrimination Learning↗
PubMed1981

Mistracking in alignment illusions.

A number of anomalies have been pointed out in opposition to attempts to account for the Poggendorff illusion in terms of the expansion of small or medium-sized acute angles. A principle under which these anomalies could be subsumed was proposed and subjected to experimental testing using simplified displays. The following theory emerged from these experiments. If a straight line (the pointer) is aligned with a do (the target) situated at the end of a second line (the induction line) and lying in a different orientation from the pointer, then (depending on the angle between pointer and induction line) the pointer will appear to be aligned with a point further along the induction line. The amount of misalignment varies inversely with increase in size, up to about 135 degrees, of the angle formed by the pointer with the induction line, after which there is no displacement attributable to the induction line. The effect appears not to be due to neural interaction. An explanation in terms of eye movement is discussed.

Discrimination Learning↗