Aging and the Perception of Motion-Defined Form

A single experiment required 26 younger and older adults to discriminate global shape as defined only by differences in the speed of stimulus element rotation. Detection of the target shape required successful perceptual grouping by common fate. A considerable adverse effect of age was found: In order to perceive the target and discriminate its shape with a d’ value of 1.5, the older observers needed target element rotational speeds that were 23.4% faster than those required for younger adults. In addition, as the difference between the rotation speeds of the background and target stimulus elements increased, the performance of the older observers improved at a rate that was only about half of that exhibited by the younger observers. The results indicate that while older adults can perceive global shape defined by similarity (and differences) in rotational speed, their abilities are nevertheless significantly compromised.

Attention to perceive, to learn and to respond

Mackintosh and his collaborators put forward an account of perceptual learning effects based, in part, on learned changes in stimulus salience. In the workshop held to mark Mackintosh’s retirement, and published as a special issue of this journal, Hall discussed Mackintosh’s theory and proposed his own alternative account. We now want to take the story forward in the light of findings and theoretical perspectives that have emerged since then. Specifically, we will argue that neither Mackintosh nor Hall was correct in his account of the principles that govern how changes in salience occur. Both supposed (in different ways) that such changes depend on the way in which the stimulus (or stimulus element) is predicted by another event. In contrast, theories of attentional learning have stressed the notion that changes in the properties of a stimulus might depend on the way in which it predicts its consequences. These theories have been concerned with attention-for-learning (associability). We now consider how the general principle they both employ might be relevant to the other forms of attention (for perception and for performance) that are, we will argue, critical for the perceptual learning effect.

Induced Motion

Induced motion is the perception of an illusory motion component in one object or stimulus element due to the presence of another object moving truly in the opposite direction. The phenomenon has been known for several centuries, having been reported in both natural scenes and reproduced in laboratory experiments. Despite the ubiquity of induced motion, attempts to explain the phenomenon have generally revolved around very few principles. Foremost among these is the notion of object-centered reference frame, which stipulates that the visual system encodes objects relative to each other rather than in absolute coordinates relative to an observer. This chapter discusses this phenomenon.

Human Classical Conditioning of Visual Compound Stimuli in Paired-Associate Tasks

College students in introductory psychology participated in four experiments to investigate the salience of color versus figure elements of paired associates. The study also reviewed the process of learning paired associates within the context of first-order simultaneous classical conditioning. In Exp. 1, four separate classes received different treatments concerning the position and type of stimulus element (color of figure) they were instructed to recall. There were seven trials with a 30-min. delay between the sixth and seventh trials. The results indicated that the groups who were required to remember the figure element of the pairs, significantly out-performed the color groups and also learned the pairs much faster. Also, there was a sharp rise in mean correct responses remembered after a 30-min. delay for the group required to recall the color element of the paired associates. Exp. 2 was a within-subjects comparison of the effectiveness of the color and figure elements as stimuli. Again, the figures elicited more correct responses than colors. Exp. 3 tested the effectiveness within subjects of the stimulus elements as response factors. As responses, however, there were no significant differences in the number of correct answers when recalling color or figure elements until the 30-min. delay between Trials 6 and 7. As expected in Exp. 4, figures elicited significantly more functional descriptions than did colors, suggesting that figures possess a logographic nature which acts as a mnemonic device aiding in the memory of stimuli and responses.

The discriminative stimulus properties of an ethanol-nicotine mixture in rats

Sprague-Dawley rats were trained to discriminate between saline (SAL) and an ethanol-nicotine mixture (0.5 g/kg ethanol plus 0.5 mg/kg nicotine) administered 15 min prior to a 15-min drug discrimination training session under a FR-10 schedule of reinforcement. The mixture dose ratio was adjusted after training to obtain a drug mixture with which both individual drugs contributed about equally to the stimulus control (1.0 g/kg ethanol plus 0.3 mg/kg nicotine). The animals were then retrained for 32 sessions using this new mixture. After training, neither nicotine nor ethanol, when tested singly, engendeded > 90% mixture-appropriate responding up to test doses that suppressed responding. Complete generalization occurred when the training doses of either nicotine or ethanol were administered in combination with various doses of the alternate drug element. (+)Nicotine, amphetamine and caffeine engendered dose-dependent increases in responses emitted on the mixture-appropriate lever. Pentobarbital and chloral hydrate only partially generalized to the training mixture. However, depressant/stimulant combinations of chloral hydrate+caffeine and pentobarbital+amphetamine produced complete generalization. The data suggest: (1) drug mixtures are not normally perceived as new entities distinct from their component elements; (2) training dose ratio may influence the characteristics of mixture discriminations; (3) stimulus element saliency may be a factor determining the nature of discriminative control by drug mixture cues; and (4) the ethanol-nicotine cue was most likely based on non-specific depressant/stimulant effects of these drugs.

Behavioural Contrast and Autoshaping

This experiment was designed to investigate the importance of autoshaping to a signal for reinforcement in the production of behavioural contrast. Two groups of pigeons were given discrimination training on a mult VI-EXT schedule: the stimuli present in the two schedule components shared common attributes, but were distinguished by the presence or absence of a visual feature. For one group (the feature positive group) the feature signalled the availability of reinforcement. For the other group (the feature negative group) the feature signalled nonrein-forcement, and for this group there was no stimulus element which unambiguously signalled reinforcement. The feature positive group showed a higher response rate during the VI component of the mult VI-EXT schedule than the feature negative group. This finding was interpreted as support for the autoshaping explanation of behavioural contrast. The results differed from those of Jenkins and Sainsbury (1969, 1970) in that both the feature positive and the feature negative groups showed discrimination learning.

Eye Fixations and Latency in a Simplified Search Situation

A technique was developed for photographing simultaneously a stimulus field and the points on the field where Ss fixated while searching for a particular stimulus element. The technique used a beam of infrared light reflected from the cornea. The stimulus elements were a single row of solid black circles, with a solid black triangle typically replacing one of the circles. The number of elements in the row and the position of the triangle in the row appeared in a random order from trial to trial. The experiment measured the number of eye fixations made during the search; it also measured the latency of the locating response. The principal result was that these two measures corresponded closely when plotted against the position of the critical element in the row.

Recall of Nonsense Sentences and Self-Reliance

60 Ss first heard 20 complete nonsense sentences read on tape and then attempted to recall the correct response element for each sentence after hearing only the stimulus element. The sentences were constructed so that response elements were incongruent with stimulus elements. Half of the sentences were judged by separate groups of judges as interesting and half as uninteresting. Ss who scored high in self-reliance recalled significantly more interesting nonsense sentence elements than those who scored low in self-reliance. Highly self-reliant Ss also recalled more uninteresting nonsense than low self-reliant Ss but the difference was not statistically significant.