Effect of visual-verbal load and spatial compatibility on stimulus response

This study examined the effects of visual-verbalload (as measured by a visually presented reading-memory task with three levels) on a visual/auditory stimulus-response task. The three levels of load were defined as follows: "No Load" meant no other stimuli were presented concurrently; "Free Load" meant that a letter (A, B, C, or D) appeared at the same time as the visual or auditory stimulus; and "Force Load" was the same as "Free Load," but the participants were also instructed to count how many times the letter A appeared. The stimulus-response task also had three levels: "irrelevant," "compatible," and "incompatible" spatial conditions. These required different key-pressing responses. The visual stimulus was a red ball presented either to the left or to the right of the display screen, and the auditory stimulus was a tone delivered from a position similar to that of the visual stimulus. Participants also processed an irrelevant stimulus. The results indicated that participants perceived auditory stimuli earlier than visual stimuli and reacted faster under stimulus-response compatible conditions. These results held even under a high visual-verbal load. These findings suggest the following guidelines for systems used in driving: an auditory source, appropriately compatible signal and manual-response positions, and a visually simplified background.     

Conditioned suppression of an avoidance response by a stimulus paired with food

Three food-deprived Long-Evans rats were exposed to a non-discriminated shock avoidance procedure. Superimposed upon this operant avoidance baseline were periodic presentations of a conditioned stimulus that was paired with food, the unconditioned stimulus. These pairings resulted in increases in the rate of shock over that recorded when the conditioned stimulus was not present. A traditional suppression ratio failed to reveal any differential effect of the conditioned stimulus on the overall rate of avoidance responding, although all subjects showed a consistent pattern of pausing and postshock response bursts during presentations of the conditioned stimulus. When food was withheld during a final extinction phase, the conditioned stimulus ceased to occasion increases in shock rates and disruptive postshock response bursts were eliminated. An analysis of conditioned suppression procedures is proposed that stresses not only operant-Pavlovian or appetitive-aversive incompatibility, but also the manner in which the baseline schedule of reinforcement affects operant behavior changes that are elicited by the superimposed Pavlovian procedure.     

Fear decrement to anxiety hierarchy items—Effects of stimulus intensity

The effects of hierarchy item intensity and duration of presentation on intra-item fear decrement were assessed with regard to systematic desensitization. Forty-eight color slides of snakes were scaled and ranked for anxiety value with the psychophysical technique of magnitude estimation by 30 female snake phobics using two response methods: verbal report and a non-verbal report instrument, the hand dynamometer. Seven test slides, spanning the scale range, were shown for 257 sec to 42 additional subjects who rated their fear level on 10 separate occasions using the hand dynamometer and verbal report. For all slides significant fear decrement occurred as a function of duration and the fear decrement across time was greater for slides of higher intensity. Negative exponential functions with similar slopes were found to fit the data for each of the slides, indicating that for each slide the same percentage of the total amount of fear decrement was lost per unit of time. The implications of these results and techniques are discussed for desensitization theory, research and therapeutic procedure.     

Explicit authenticity and stimulus features interact to modulate BOLD response induced by emotional speech

Context has been found to have a profound effect on the recognition of social stimuli and correlated brain activation. The present study was designed to determine whether knowledge about emotional authenticity influences emotion recognition expressed through speech intonation. Participants classified emotionally expressive speech in an fMRI experimental design as sad, happy, angry, or fearful. For some trials, stimuli were cued as either authentic or play-acted in order to manipulate participant top-down belief about authenticity, and these labels were presented both congruently and incongruently to the emotional authenticity of the stimulus. Contrasting authentic versus play-acted stimuli during uncued trials indicated that play-acted stimuli spontaneously up-regulate activity in the auditory cortex and regions associated with emotional speech processing. In addition, a clear interaction effect of cue and stimulus authenticity showed up-regulation in the posterior superior temporal sulcus and the anterior cingulate cortex, indicating that cueing had an impact on the perception of authenticity. In particular, when a cue indicating an authentic stimulus was followed by a play-acted stimulus, additional activation occurred in the temporoparietal junction, probably pointing to increased load on perspective taking in such trials. While actual authenticity has a significant impact on brain activation, individual belief about stimulus authenticity can additionally modulate the brain response to differences in emotionally expressive speech.     

Effect of familiarity and category contrast on stimulus and response priming

In a letter-symbol classification task, flanking incompatible symbols slowed response latencies to letter targets, whereas incompatible letter flankers did not slow the classification of symbol targets. The conditions surrounding this asymmetry in response competition were investigated in five experiments. The results showed that: (1) the asymmetry was not related to the familiarity of the symbol targets or to the prime-target interval; (2) when the classification involved familiar and unfamiliar symbols, the asymmetry remained (i.e., there was less interference associated with the unfamiliar symbol targets), but there was now significant response competition associated with both symbol categories; and (3) with a mixed-category task (i.e., letters and symbols assigned to both responses), the symbol targets continued to be less interfered with by both letter and symbol incompatible flankers. These findings were interpreted as suggesting that response competition can be influenced by both classification decision rules and cohesiveness of exemplars comprising a category.     

Effect on of familiarity and category contrast stimulus and response priming

In a letter-symbol classification task, flanking incompatible symbols slowed response latencies to letter targets, whereas incompatible letter flankers did not slow the classification of symbol targets. The conditions surrounding this asymmetry in response competition were investigated in five experiments. The results showed that: (1) the asymmetry was not related to the familiarity of the symbol targets or to the prime-target interval; (2)when the classification involved familiar and unfamiliar symbols, the asymmetry remained (i.e., there was less interference associated with the unfamiliar symbol targets), but there was now significant response competition associated with both symbol categories; and (3) with a mixed-category task (i.e., letters and symbols assigned to both responses), the symbol targets continued to be less interfered with by both letter and symbol incompatible flankers. These findings were interpreted as suggesting that response competition can be influenced by both classification decision rules and cohesiveness of exemplars comprising a category.     

Pentylenetetrazole as an unconditioned stimulus for olfactory and contextual fear conditioning in rats

The association of five footshocks with a neutral odor is able to establish an olfactory fear conditioning in rats. The present study sought to investigate whether the systemic administration of pentylenetetrazole (PTZ; 3.75–15 mg/kg) would turn the coffee odor in a conditioned stimulus in the fear conditioning paradigm. The results showed that rats started to display risk assessment and avoidance after PTZ (15 mg/kg)–coffee odor pairing. When three mild footshocks (0.4 mA for 2 s) were delivered during this pairing, the conditioned response exhibited was greater than before. In both cases, however, pretreatment with the benzodiazepine midazolam (MDZ. 0.5 mg/kg i.p.) fully counteracted the expression of these defensive behaviors. Moreover, after being paired with 15 mg/kg of PTZ alone or combined with footshocks, the coffee odor was able to promote a new fear conditioning related to the context where it was re-exposed. The present findings point out the usefulness of PTZ as an unconditioned stimulus to promote fear conditioning to olfactory and contextual cues in rats.     

Probability effects on stimulus evaluation and response processes.

This study investigated the effects of probability information on response preparation and stimulus evaluation. Eight subjects responded with one hand to the target letter H and with the other to the target letter S. The target letter was surrounded by noise letters that were either the same as or different from the target letter. In 2 conditions, the targets were preceded by a warning stimulus unrelated to the target letter. In 2 other conditions, a warning letter predicted that the same letter or the opposite letter would appear as the imperative stimulus with .80 probability. Correct reaction times were faster and error rates were lower when imperative stimuli confirmed the predictions of the warning stimulus. Probability information affected (a) the preparation of motor responses during the foreperiod, (b) the development of expectancies for a particular target letter, and (c) a process sensitive to the identities of letter stimuli but not to their locations.     

Decrements in olfactory sensitivity due to ozone exposure.

Approximate olfactory thresholds were determined in an exploratory study in which subjects were exposed to ozone (O3). The odorants were butyl alcohol (BA) and acetic acid (AA). Preliminary data suggest (1) temporary increases in thresholds due to O3 exposure, (2) diminution of O3 effects with repeated exposures, and (3) greater and more reliable effects for BA than for AA.     

The interactive effects of stimulus generalization decrement and contextual pre-exposure cues upon fear incubation

Models of fear incubation may be described as explanations for the interference of Pavlovian extinction. From this perspective, the effects of several parameters upon the incubation phenomenon were examined. Fear incubation was found to be attenuated by manipulations associated with stimulus generalization decrement (Experiment 1), as well as pre-exposure manipulations (Experiment 2). These findings were incorporated within existing models of incubation.     

Preconditioning exposure to the unconditined stimulus affects the acquisition of a conditioned emotional response

Four experiments examined the UCS preexposure phenomenon using conditioned suppression of food-reinforced responding as a measure of excitatory conditioning, and electric shock as a UCS. In Experiment 1, groups of rats were preexposed to unsignaled 0.8-mA electric shocks for 0, 1, 3, 5, or 10 days, and then conditioned with a 0.8-mA electric shock. Preexposure to electric shock 1 day prior to conditioning enhanced the acquisition of a CER, whereas preexposure to electric shock for 3, 5, or 10 days prior to conditioning attenuated the acquisition of a CER as a direct function of the number of days of preexposure. In Experiments 2 and 2A, groups of rats were preexposed to unsignaled electric shocks of 0.3, 0.5, 0.8, or 1.3 mA for 10 days, and then conditioned with a 0.8-mA electric shocl. All groups preexposed to electric shock acquired the CER at a slower rate than a group not preexposed to electric shock. The greatest attenuation of CER conditioning occurred when the same intensity electric shock was used during both the preexposure and conditioning phases. In Experiment 3, groups of rats were preexposed to signaled electric shocks of either 0.5, 0.8, or 1.3 mA, and then conditioned with a 0.8-mA electric shock. All groups preexposed to electric shock acquired the CER at a slower rate than a group not preexposed to electric shock. As in Experiments 2 and 2A, the greatest attenuation of CER conditioning occurred when the same intensity electric shock was used during both the preexposure and conditioning phases. In Experiment 4, groups of rats were preexposed to series of 0.5, 0.8, or 1.3-mA electric shocks which they could escape by performing a chain-pull response. Rats in each of these groups had yoked partners which received the same number, intensity, and temporal pattern of electric shocks, but could not perform a response to escape shock. All groups were then conditioned with a 0.8-mA electric shock. Rats preexposed to escapable electric shocks showed equal or greater attenuation of CER conditioning than rats which could not escape shock during the preexposure phase. These results are discussed in terms of nonassociative and associative explanations of the UCS preexposure phenomenon.     

Behavioral decrement following stimulus preexposure: effects of number of preexposures, presence of a second stimulus, and interstimulus interval in children and adults.

This article presents an analysis of the similarities between the stimulus familiarization effect and latent inhibition. Just as latent inhibition has been readily demonstrated in infrahumans, and only with considerable difficulty in adult humans, the experiments reported here obtained a significant interaction between the stimulus familiarity effect and age. Children exhibited increased reaction time to preexposed stimuli as opposed to nonpreexposed stimuli, but adults did not show this effect. In addition, a number of variables were shown to affect the amount of decrement. The decrement increased as a function of the number of preexposures and decreased with the addition of a second stimulus placed in a conditioning relationship to the to-be-tested stimulus during preexposure. However, an increased in the interstimulus interval was only marginally effective in increasing the inhibitory effects of preexposure. The data were discussed in relation to a conditioned attention explanation for these phenomena of behavioral decrement.     

Effect of an auditory stimulus on the processing of a visual stimulus under single- and dual-tasks conditions

The Sternberg Additive Factor Method was used to draw inferences about the flow of information under single- and dual-tasks conditions which were identical in terms of the stimuli involved but different in terms of response requirements. In both conditions, subjects pressed a left- or right-hand key in response to the onset of an X or O (intact or degraded) which was accompanied by a monaural or binaural tone. In the dual-tasks condition, subjects responded verbally to the tone location while also making the key-press response, whereas, in the single-task condition, no response to the tone was required. The pattern of main effects and interactions suggested that the same model of information flow described both single- and dual-tasks conditions; i.e., visual and auditory stimuli were encoded separately but shared capacity at the response selection stage.     

The influence of irrelevant stimulus changes on stimulus and response repetition effects

In this study the influence of irrelevant stimulus changes from one trial to another in a serial reaction time task was investigated. Two experiments were performed in which subjects were required to respond to stimulus colour. Four colours were mapped on two response keys, so that colour and response repetition effects could be dissociated. In Experiment 1, the irrelevant stimulus dimension was location and in Experiment 2 it was shape. Both experiments were performed with a short and a long response-stimulus interval (RSI)-condition. In both experiments, the irrelevant dimension influenced the response repetition effect but not the colour repetition effect. In the reaction times, a response alternation effect was observed only when the irrelevant location of the stimulus changed in the long RSI-condition. The error rates showed a response alternation benefit for both irrelevant dimensions, in the short and the long RSI-condition. The benefit for response alternations is explained in terms of a response bias towards change that is triggered by a changing stimulus feature. We assume that the response bias is stronger for location than for colour and that accuracy is more sensitive to this bias than response latencies.