Simultaneous and preceding sounds enhance rapid visual targets: Evidence from the attentional blink

Presenting two targets in a rapid visual stream will frequently result in the second target (T2) being missed when presented shortly after the first target (T1). This so-called attentional blink (AB) phenomenon can be reduced by various experimental manipulations. This study investigated the effect of combining T2 with a non-specific sound, played either simultaneously with T2 or preceding T2 by a fixed latency. The reliability of the observed effects and their correlation with potential predictors were studied. The tone significantly improved T2 identification rates regardless of tone condition and of the delay between targets, suggesting that the crossmodal facilitation of T2 identification is not limited to visual-perceptual enhancement. For the simultaneous condition, an additional time-on-task effect was observed in form of a reduction of the AB that occurred within an experimental session. Thus, audition-driven enhancement of visual perception may need some time for its full potential to evolve. Split-half and test-retest reliability were found consistently only for a condition without additional sound. AB magnitude obtained in this condition was related to AB magnitudes obtained in both sound conditions. Self-reported distractibility and performance in tests of divided attention and of cognitive flexibility correlated with the AB magnitudes of a subset but never all conditions under study. Reliability and correlation results suggest that not only dispositional abilities but also state factors exert an influence on AB magnitude. These findings extend earlier work on audition-driven enhancement of target identification in the AB and on the reliability and behavioural correlates of the AB.     

Coarse guidance by numerosity in visual search

In five experiments, we examined whether the number of items can guide visual focal attention. Observers searched for the target area with the largest (or smallest) number of dots (squares in Experiment 4 and “checkerboards” in Experiment 5) among distractor areas with a smaller (or larger) number of dots. Results of Experiments 1 and 2 show that search efficiency is determined by target to distractor dot ratios. In searches where target items contained more dots than did distractor items, ratios over 1.5:1 yielded efficient search. Searches for targets where target items contained fewer dots than distractor items were harder. Here, ratios needed to be lower than 1:2 to yield efficient search. When the areas of the dots and of the squares containing them were fixed, as they were in Experiments 1 and 2, dot density and total dot area increased as dot number increased. Experiment 3 removed the density and area cues by allowing dot size and total dot area to vary. This produced a marked decline in search performance. Efficient search now required ratios of above 3:1 or below 1:3. By using more realistic and isoluminant stimuli, Experiments 4 and 5 show that guidance by numerosity is fragile. As is found with other features that guide focal attention (e.g., color, orientation, size), the numerosity differences that are able to guide attention by bottom-up signals are much coarser than the differences that can be detected in attended stimuli.     

Retrieval-induced forgetting and unwanted thought intrusions

The act of retrieving an existing memory has been found to inhibit the recall of related memories, a phenomenon known as retrieval-induced forgetting (RIF). The purpose of the present study was to investigate the hypothesis that individuals with a strong RIF effect might be better at suppressing unwanted intrusive thoughts. In Experiment 1 the relationship between RIF and the prevalence of intrusive thoughts was investigated using a sample of 58 normal British participants, who completed three different questionnaires to measure their susceptibility to intrusive thoughts, obsessional thoughts, and impulsive thoughts. Their susceptibility to RIF was also measured, using the standard procedure introduced by Anderson, Bjork, and Bjork (1994). The results showed a significant RIF effect, and, although no significant correlations were found between RIF strength and any of the three measures of intrusive thoughts, there was some evidence to suggest a possible relationship between RIF and intrusive thoughts. In an effort to clarify these inconclusive findings, Experiment 2 investigated the relationship between RIF and intrusive thoughts in a different and more varied population sample, consisting of 90 normal members of the Greek population. Experiment 2 confirmed the RIF effect, but no significant association was found between RIF and intrusive thoughts. These findings therefore offer no support for the hypothesis that RIF assists the suppression of intrusive thoughts in normal individuals.     

Imitation in rats: Initial responding and transfer evidence

In two experiments, rats observed a conspecific demonstrator pushing a single manipulandum, a joystick, to the right or to the left for food reward before being given access to the joystick, for the first time, from a different orientation. In Experiment 1, rats that had observed left-pushing made more of their first three responses to the left than did rats that had observed right-pushing. In Experiment 2 the axis of joystick movement was rotated through 90° between observation and testing for half of the animals. These rats, like those that were tested with the joystick in the position it had occupied during demonstrator responding, showed a significant tendency to push the joystick in the same direction relative to their own bodies as had their demonstrators. These results, which cannot be explained in terms of stimulus-reinforcer learning, provide evidence that rats are capable of imitation, i.e. response, or response-reinforcer, learning by observation.     

Performance on ratio and interval schedules with matched reinforcement rates

In the first study, rats were trained to pull a chain on a schedule (RPI) that regulates the probability of reinforcement to maintain a constant average reinforcement rate without differentially reinforcing long inter-response times (IRTs). Although the response rate was sensitive to the overall rate of reinforcement, performance was unaffected by variations between 1 and 50 in the IRT memory size used in programming the schedule. In the second study, two groups of animals performed on either a random-interval (RI) schedule or a RPI schedule, with reinforcement rates determined by those generated by a third group performing on a random ratio (RR) 20 schedule. The RI group responded at a lower rate than the RPI group, which, in turn, responded at a lower rate than the RR group, even though the three groups experienced comparable rates of reinforcement. The fact that the RPI group responded at a lower rate than the RR group suggests that the standard response rate difference observed between ratio and interval schedules, which have been matched for reinforcement rate, cannot be attributed solely to the fact that conventional interval schedules differentially reinforce long IRTs.     

Why are there eccentricity effects in visual search? Visual and attentional hypotheses

In standard visual search experiments, observers search for a target item among distracting items. The locations of target items are generally random within the display and ignored as a factor in data analysis. Previous work has shown that targets presented near fixation are, in fact, found more efficiently than are targets presented at more peripheral locations. This paper proposes that the primary cause of this “eccentricity effect” (Carrasco, Evert, Chang, & Katz, 1995) is an attentional bias that allocates attention preferentially to central items. The first four experiments dealt with the possibility that visual, and not attentional, factors underlie the eccentricity effect. They showed that the eccentricity effect cannot be accounted for by the peripheral reduction in visual sensitivity, peripheral crowding, or cortical magnification. Experiment 5 tested the attention allocation model and also showed that RT X set size effects can be independent of eccentricity effects. Experiment 6 showed that the effective set size in a search task depends, in part, on the eccentricity of the target because observers search from fixation outward.