Attention in visual search: Multiple search classes

Data from visual-search tasks are typically interpreted to mean that searching for targets defined by feature differences does not require attention and thus can be performed in parallel, whereas searching for other targets requires serial allocation of attention. The question addressed here was whether a parallel-serial dichotomy would be obtained if data were collected using a variety of targets representing each of several kinds of defining features. Data analyses included several computations in addition to search rate: (1) target-absent to target-present slope ratios; (2) two separate data transformations to control for errors; (3) minimum reaction time; and (4) slopes of standard deviation as a function of set size. Some targets showed strongly parallel or strongly serial search, but there was evidence for several intermediate search classes. Sometimes, for a given target-distractor pair, the results depended strongly on which character was the target and which was the distractor. Implications from theories of visual search are discussed.     

Importance of precue location in directing attention

In location-precuing experiments, accuracy in discrimination of T-like characters improves with increasing time between the precue and the target. In this experiment, two central and two peripheral cue locations were examined using 13 different cue-target intervals from 0 to 234 msec. Accuracy was the same when trials were cued from the two peripheral locations (two thirds distance between fixation and target or distal to the target location). Centrally cued trials (cues at fixation or next to fixation) resulted in slower onset of attentional effects than peripherally cued trials, but there was greater accuracy at long cue-target intervals for central than for peripheral cues. Data are compared to previously published research.     

Schedule-induced polydipsia in rats living in an operant environment

The effect of variations in interreinforcement interval on the temporal and distributional relation between feeding and drinking was continuously monitored. Rats were housed continuously in an operant chamber in which water was freely available, but lever pressing was required to obtain food (45-mg pellets). Initially, pellets were delivered on a fixed-ratio 1 schedule of reinforcement, which was followed by testing on response-initiated fixed-interval 15-, 30-, and 60-second schedules. The total number of discrete, daily meals (a period in which several pellets were earned in succession) was slightly higher during the fixed-interval schedules than during the fixed-ratio 1, but there was no systematic effect of fixed-interval length on meal frequency. Total water consumption, in contrast, increased dramatically as the interval was lengthened: both subjects consumed two to three times as much water on the fixed-interval 60-second schedule as on the fixed-ratio 1. The increased water consumption was the result of an alteration in the distribution of drinking relative to eating. During the fixed-ratio 1 condition, drinking occurred infrequently following individual food pellets and represented the smallest percentage of total drinking; drinking occurred predominantly just before or after a meal. As the fixed interval was lengthened, however, the frequency of postpellet drinking gradually increased and eventually comprised the largest proportion of daily drinking.     

Why ‘Is’ Must Entail ‘Ought’

I argue below for the view that non-moral truths entail moral ones. I first argue that moral claims do have truth values which are objectively true or false. I then argue that this objectivism does not entail non-relativism. I produce a simple possible worlds argument for the entailment view. I then give some examples where p entails q but many intelligent people have thought it does not, and where it does not, but many intelligent people have thought that it does. I also try to evaluate a somewhat neglected argument by Hume. In the final section, I further consider some moral and meta-moral opinions.     

Testing alternative explanations for mortality salience effects: Terror management,value accessibility,or worrisome thoughts?

Previous research has shown that reminding subjects of their mortality encourages negative reactions to others whose behaviour or attitudes deviate from the cultural worldview (e.g. Greenberg, Pyszczynski, Solomon, Rosenblatt, Veeder, Kirkland and Lyon 1990; Greenberg, Simon, Pyszczynski, Solomon and Chatel 1992; Rosenblatt, Greenberg, Solomon, Pyszczynski and Lyon 1989). According to terror management theory, these findings result from a heightened need for faith in the cultural worldview that is activated by reminders of one's mortality. Study I assessed the plausibility of an alternative explanation which posits that mortality salience simply primes individuals' values. Whereas mortality salience led to harsher bond recommendations for a prostitute, a procedure that directly focused subjects on their values did not. Studies 2 and 3 assessed the possibility that reminding subjects of any worrisome future concern would produce the same effect as a reminder of mortality. In both studies, mortality salience led to negative reactions to a deviant and had no effect on self-reported affect, whereas other worrisome thoughts had no effect on reactions to a deviant but did create negative affect. Thus, consistent with terror management theory, mortality salience effects seem to result exclusively from thoughts of death.     

Pavlovian conditioning of shock-elicited aggression: a discrimination procedure

Two auditory stimuli, separated by a fixed intertrial interval, were alternately presented to two rats in a closed environment. The positive conditioned stimulus (CS+) terminated with the offset of a 2-mA, 0.75-sec shock. The negative conditioned stimulus (CS-) terminated without shock. The incidence of the "stereotyped fighting posture" was recorded during the CS+, the CS-, the intertrial interval, and shock. The results showed an increase in the percentage of conditioned responses during the CS+, and a decrease during both the CS- and the intertrial interval, when the duration of the conditioned stimuli and the intertrial interval was 16 sec. Appropriate changes in the incidence of aggression during the two stimuli were obtained following the reversal of the stimulus functions. During the acquisition and reversal phases there was a between-session decrement and a within-session improvement in the incidence of aggression during the CS+, defined as warm-up. The presentation of free shocks before the conditioning sessions was effective in reducing the warm-up only when the interval between shocks was 64 sec. These data were interpreted as demonstrating classical conditioning of shock-elicited aggression, with little chance of non-associative factors contributing to the measurement of the conditioned response.     

Some notes on conditioned suppression and reinforcement schedules

Two pigeons were trained on an FR 150 schedule of reinforcement. An Estes-Skinner conditioned suppression procedure was then superimposed on this performance at varied intervals. If the CS occurred during the early stages of the ratio run, complete suppression resulted. If the CS occurred during the later stages of the run, the birds continued to respond until the reinforcement was obtained, which was then followed by complete suppression.     

Large and rapid improvement in form discrimination accuracy following a location precue

Processing of a visual stimulus can be improved by precuing its location. Most previous precue studies have used reaction time as the dependent measure and have found large effects; but when form discrimination accuracy has been used, precue effects have been relatively small. The present experiments yielded large, short-latency precue effects on form discrimination accuracy. A small square precue was briefly presented near one of four possible target locations. Then one of four possible targets (T-like figures) was presented in each location, followed by a mask. Observers attempted to identify the target that had been presented in the cued location. In experiment 1, target duration, cue-to-target distance, and cue-target onset asynchrony (SOA) were varied. Target discriminability (d') increased markedly with increasing precue-target SOA, even at very short SOAs. Thus, there was no evidence for a delay in the onset of precue effects (caused, for example, by the need to shift attention across the visual field). Performance was best for precues that were closest to the target, thus ruling out a forward masking explanation of the effect. Finally SOA and target duration interacted strongly - longer precue SOAs resulted in larger effects of target duration. In experiment 2, this interaction was replicated using an additional target duration and longer SOAs. One interpretation of this result is that focal attention increases the rate at which information can be extracted from a visual location.