Parts of visual objects: an experimental test of the minima rule

Three experiments were conducted to test Hoffman and Richards's (1984) hypothesis that, for purposes of visual recognition, the human visual system divides three-dimensional shapes into parts at negative minima of curvature. In the first two experiments, subjects observed a simulated object (surface of revolution) rotating about a vertical axis, followed by a display of four alternative parts. They were asked to select a part that was from the object. Two of the four parts were divided at negative minima of curvature and two at positive maxima. When both a minima part and a maxima part from the object were presented on each trial (experiment 1), most of the correct responses were minima parts (101 versus 55). When only one part from the object--either a minima part or a maxima part--was shown on each trial (experiment 2), accuracy on trials with correct minima parts and correct maxima parts did not differ significantly. However, some subjects indicated that they reversed figure and ground, thereby changing maxima parts into minima parts. In experiment 3, subjects marked apparent part boundaries. 81% of these marks indicated minima parts, 10% of the marks indicated maxima parts, and 9% of the marks were at other positions. These results provide converging evidence, from two different methods, which supports Hoffman and Richard's minima rule.     

Primary-school stutterers: Have attitudes changed?

How concerned are primary-school-aged stuttering children about their communication problem? What are the clinical implications of this concern?Fifteen years ago, Silverman (1970) suggested that primary-school-aged children who stuttered were not concerned about their disfluencies. A clinical implication of that report was that the interpreted lack of concern might negatively affect the children's motivation and desire for change in therapy. Scant research exists to support or refute this implication. While research is available on reactions to stuttering, pretherapeutic attitudes—especially those of children—have not been systematically reported. Guitar (1976) measured the pre-treatment attitudes of 38 adult stutterers and reported that, “those stutterers with more negative attitudes measured just prior to treatment, were most likely to have high levels of stuttering a year later, even though all subjects left therapy entirely fluent.” In related areas, research by Kolb, Winter, and Berlen (1968), McFall (1970), and McFall and Hammen (1971) has indicated that clients who are more motivated do better in behavior modification programs.Whether or not these findings may be generalized to children, in the midst of a developmental process, is purely speculative.     

Reflex modification in the rat: the inhibitory effects of intensity and frequency changes in steady tones

In laboratory rats (as in humans) a low-intensity tone that precedes a high-intensity burst of noise by approximately 100 ms can reduce the amplitude of the startle reaction elicited by the burst of noise. A series of four experiments with rats investigated the relation between the inhibitory effects of tonal frequency change and the length of the silent period (gap) preceding it. The major findings were the following: (a) A gap in an otherwise continuous pure tone inhibited startle when the gap occurred approximately 100 ms prior to the noise burst. (b) Although an increase in gap duration increased the inhibition afforded by the gap, the maximum inhibition was yielded by gaps of 100 ms and greater; this maximum was equivalent to the inhibition yielded by the presentation of a postgap tone alone. (c) A shift in tonal frequency across a 10-ms gap yielded more inhibition than did the same gap with no frequency shift; again the shift yielded equivalent inhibition to the presentation of the postgap tone alone. (d) An increase in the frequency shift increased inhibition when the shift occurred across a 10-ms gap, but not when the shift occurred across a 100-ms gap.     

Spatial attention in vision

Summary Human observers can selectively allocate processing resources to different areas of the visual field within a single fixation. This spatial attention system may affect either the quality of information extraction or the decisions and responses based on this information. This paper reviews evidence from behavioral, single-unit, and event-related potential paradigms; the evidence suggests a relatively early locus of spatial attention.This research was supported by the U. S. Army Research Office under contract DAAG 29-83-K-0049. Portions of this paper were presented to the Conference on Attention and Action, Bielefeld, West Germany, in July 1985     

Book reviews

With Faith and Fury. Delos McKown. New York: Promethius Books, 1985. pp 440. $16.95

The Sacred in a Secular Age. Phillip E. Hammond, Editor. University of California Press, 379 pages (p/b) $8.95 (£8.50)     

Tonal frequency shifts and gaps in acoustic stimulation as reflex-modifying events

When a relatively weak signal, such as a mild tone, precedes an intense reflex-eliciting stimulus by an appropriate interval (about 100 msec), the amplitude of the elicited reaction is often reduced. It was found that in student volunteers a brief gap in a steady pure tone that occurred 150 msec prior to a mild tap to the glabella (the flat region between the eyebrows) could inhibit the eyeblink elicited by the tap. It was also found that a shift in tonal frequency across a gap in a tone was more inhibitory than a gap with no frequency shift, but it was no more inhibitory than the onset of the short second tone alone. The final study determined the minimum amount of frequency shift required to produce an additional inhibitory effect above that of a gap alone. The findings are discussed in terms of various aspects of sensory processing.     

Political Waffling: Its Effects on the Evaluations of Observers1

Politicians sometimes shift the stances that they take on issues. An experiment investigated the effect of such a shift upon observers' perceptions of and feelings about an ostensible candidate for public office. The target issue (private ownership of handguns) was chosen as being relatively emotional for some subjects and unemotional for others. Subjects were also selected (independently) as being either pro or con on the issue. The position taken by the stimulus person (who, in contrast to previous research, was identified as a candidate for office) was portrayed as initially being either similar or dissimilar to that of the subject. An assessment of the candidate's position 6 months later indicated either no change or a reversal of the initial position. Subjects' evaluations of the candidate on a variety of dimensions yielded a consistent pattern. The combination of initial agreement and final agreement was viewed more favorably than any other combination. Taken together, the data suggest two conclusions. First, there was no support in this context for the notion that a shift from disagreement to agreement would be especially valued (i.e., there was no “gain” effect). Second, in the realm of politics, people value consistent agreement with their own position—but they do not reward consistency per se.     

Active-interactional cotherapy

In the literature on cotherapy, little attention has been focused on maximizing the effectiveness of two therapists working in tandem with families and couples. While cotherapists may at times share their ideas and feelings with their clients, and after the therapeutic session exchange views between themselves, generally little interaction occurs between them during the session. In this paper, a case is presented for more active interactions between cotherapists during the session, in order to expedite and facilitate change and growth in their clients. Anecdotal examples are provided to illustrate the approach.