Theodore E. Parks

Thatcher and the Cheshire Cat: Context and the Processing of Facial Features

As has been noted before, a face made gruesome by the inversion of its mouth will not be so perceived when the entire construction is inverted. Results are presented which suggest that this is because (a) the mouth and eye features are evaluated individually (although each feature may influence the evaluation of the other) and (b) the mouth, whether normal or inverted, tends to have its uppermost part assigned as ‘top’, providing for either a pleasant smiling-mouth expression or a gruesome ‘biting-intention’ expression. However, the gruesomeness of an inverted mouth is attenuated when eyes are shown below it (producing an inverted smiling face) which suggests that the location of other facial features can also influence the assignments of ‘top’.

Subjective Figures: Some Unusual Concomitant Brightness Effects

Black-on-white displays are presented which are capable of producing subjective figures that are not enhanced in brightness.

Illusory Contour Lightness: A Neglected Possibility

When the area occupied by a typical sharp-edged illusory figure is outlined physically, some illusory lightness survives within the contours as an example of figure-ground contrast. This general phenomenon may therefore account for the direction of the apparent alteration in lightness found within many illusory figures, but it cannot account for the magnitude of that alteration.

Sharp-edged vs. diffuse illusory circles: The effects of varying luminance

As had been found previously, one experiment demonstrated that reducing the luminance of a pattern that induced an abrupt-edged illusory figure increased mean ratings of that illusory effect. More importantly, the same result had not been found for a pattern that induced a diffuse illusory figure; in fact, a second experiment with such patterns produced a reliable tendency in the opposite direction. These results are at variance with the suggestion that an abrupt-edged illusory effect involves merely a minor variation in the boundary definition of a diffuse illusory lightness effect.

The Subjective Brightness of Illusory Figures: Is Stratification a Factor?

An increase in factors which might contribute to apparent stratification was found to counteract the expected reduction in the subjective brightness of an illusory figure usually produced by decreasing the orthogonality of surrounding line segments and to enhance brightness when the degree of orthogonality was held constant.

Illusory Contours from Pictorially Three-Dimensional Inducing Elements

Illusory-figure patterns which are composed of pictorial elements representing three-dimensional partial disks are sometimes effective and sometimes not. When they are not effective, it is apparently because they contain information that contradicts the presence of an occluding figure and/or because all of the edges within the pattern are seen as edges of various pictured surfaces of the elements.

Enduring visual memory despite forced verbal rehearsal.

The ability to decide rapidly that two visual stimuli are nominally the same when they are also visually the same (the Posner effect) was examined for stimuli of increasing visual complexity (Experiment 1) and when a greater variety of visual differences between the two stimuli was employed (Experiment 2). When the two stimuli each consisted of a pair of letters or when to single-letter stimuli sometimes differed in both case and style, the Posner effect occurred even though subjects made overt verbal rehearsals of the first stimulus. The results suggest that losses of the Posner effect found under simpler circumstances are not attributable to a switch from visual to exclusively verbal coding.

Interference with Short-Term Visual Memory Produced by Concurrent Central Processing.

Double-letter memory and test stimuli were used in two experiments on a speek comparison task. Faster decision times were found when memory and test stimuli were physically identical than when they were the same in name only. This finding was true even with retention intervals as long as 12 sec and even when difficult tasks filled the retention intervals. However, the decision-time advantage of physically identical comparisons was greatest when the interval was not filled with a task likely to interfere with rehearsals. High verbal subjects had a smaller advantage for the physically identical comparisons than did low verbal subjects but were affected in the same way as low verbal subjects in terms of which conditions raised the overall correct comparison times, raised the error rates, and reduced the advantage of physically identical comparisons.

Pictorial depth and the Poggendorff illusion

An informal demonstration is offered, which strongly supports previous contentions that, when the elements of a Poggendorff display appear to be arranged in pictorial space such that the two critical line segments are at different heights, an illusory impression of misalignment may occur. A second pair of demonstrations shows, however, that such a height difference is neither a necessary nor a sufficient cause of the illusion. In addition, the harmful effect of adding certain pictorial elements to the standard Poggendorff pattern requires a new understanding.

Last but Not Least

As Richard Gregory pointed out in his recent book, Mirrors in Mind (1997), an interesting size illusion occurs when you observe yourself in an ordinary wall-mirror and ask yourself how much of the surface of the mirror you would need to blot out (with, for example, paint) in order to completely, but only, hide the image of your head. If you are standing at arms length or less, you can then test your impression by reaching out and covering that part of the mirror with your hand. The result will probably be surprising: If, for instance, you are at approximately arms length, you will find that your clenched fist is large enough. I submit that the reasons for our initial (erroneous) impression are twofold. First, because of size-scaling based upon depth cues, an impression of normal head size occurs. Second, that full-sized head appears to be on or closely within the surface of the mirror, so the impression is that a head-sized blot would be required (just as would be the case if a full-sized painting of a head were there, instead). One curiosity here is that two contradictory distances are simultaneously involved, one as the basis for successful size-scaling (to wit, twice the distance from you to the mirror) and one evoked when the image is seen to be on the mirror (to wit, just the distance to the mirror since that is where the head seems to be). I have found that this paradox can be made dramatically evident in a variant of the basic demonstration: Observe yourself in the mirror through two short cylindersöthe coiled fingers of your two hands will doösuch that the edges of the mirror (and, therefore, cues to its distance) are hidden. When these blinders are suddenly removed, your image will appear to jump towards you because the cues to the second of the two distances are, then, suddenly restored. There is an additional curiosity here: Not only will your face then look nearer, it will also look larger! Of course, this juxtaposition reminds us of the startling appearance of a newly risen moon, but there may be a deeper connection than that: the well-known size-scaling explanation for the apparently larger size of a horizon moon, while attributing the appearance to apparently greater distance, also acknowledges that that moon also looks nearer, a paradox which disappears if it is acknowledged that we may simultaneously register two different distancesöone that is involved in size-scaling and another of which we are aware.(1) Theodore E Parks Department of Psychology, University of California at Davis, Davis, CA 95616, USA; e-mail: teparks@ucdavis.edu