Latent inhibition in humans: Data, theory, and implications for schizophrenia.

Learning about the consequences of a stimulus is retarded if that stimulus has been experienced without reinforcement. A literature review of this latent inhibition (LI) effect indicates that LI is similar in human and other species, although in adult humans it often requires a masking or distracter task. The discrepancy in conditions for producing LI can be accounted for by developmental differences in the automatic processing of unattended stimuli. In adults, automatic processes are subject to a controlled information-processing override. Masking prevents controlled processing of the preexposed stimuli so that they remain unattended. The role of masking in attenuating LI in schizotypal/schizophrenic groups is assessed. It is proposed that schizophrenia is related to an inability to use occasion-setting properties of context or to switch from controlled to automatic processing of inconsequential events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition with a response time measure from a within-subject design: Effects of number of preexposures, masking task, context change, and delay.

Latent inhibition (LI), poorer performance on a learning task to a previously irrelevant stimulus than to a novel stimulus, was produced in 4 experiments, using a within-subject design and a response time (RT) measure. LI was reduced by decreasing the number of stimulus preexposures, omitting the masking task, changing the context from the preexposure to the test phase, and introducing a delay between the 2 phases. Together, these effects indicate that the within-subject RT-based LI reflects the same processes as those that govern between-subject LI with correct response as the dependent measure. The new procedure provides an advantageous method for assessing attentional dysfunction related to the processing of irrelevant stimuli, particularly in pathological groups, such as patients with schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition.

Reviews the latent inhibition literature concerning the decremental effects of nonreinforced preexposure to the to-be-conditional stimulus on subsequent learning. Latent inhibition is found to be a broadly based phenomenon appearing across a variety of species (goldfish, goat, sheep, rat, rabbit, dog, human child, and, under special conditions, the human adult) and across a variety of tasks (classical conditioning, avoidance conditioning, Ivanov-Smolensky conditioning, conditioned emotional response, go/no-go discrimination, reaction time, and conditioned taste aversion paradigms). The stability of latent inhibition as well as its stimulus specificity and the effects of number of nonreinforced preexposures are examined. Current explanations of latent inhibition which include the habituation of the orienting response, selective filtering, specific antagonistic and complementary responses, and conditioned inhibition are discussed. The need for a combined learning and attention theory is suggested. (64 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stress affects the selection of relevant from irrelevant stimuli.

Two experiments were used to examine the effects of stress on latent inhibition (LI; poorer learning with a previously exposed irrelevant stimulus rather than a novel stimulus). In Experiment 1, stress was induced in college students by threatening participants' self-esteem with a difficult number series completion test that was related to intelligence. In Experiment 2, the participants were job seekers who were either informed or not that the LI test was part of the selection process. In both experiments, LI was attenuated in high- as compared with low-stressed participants. The results suggest that stress and/or anxiety impairs the inhibition of irrelevant-preexposed stimuli. Implications for understanding the impaired selective attentional processes in schizophrenia and schizotypy are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Are high-schizotypal normal participants distractible or limited in attentional resources? A study of latent inhibition as a function of masking task load and schizotypy level

Two experiments with normal participants examined the effects of masking and masking task load on latent inhibition (LI, poorer learning for a previously exposed irrelevant stimulus than for a novel stimulus) as a function of level of schizotypality. In Experiment 1, a masking task was needed to produce LI. In Experiment 2, with low load, LI was present in low- but not high-schizotypal participants. In high load, LI was abolished in low-schizotypal participants, but only approached significance in high-schizotypal participants. The data support a distraction- rather than a resource-limitation model of attentional dysfunction in high-schizotypal normal participants. In addition, the data indicate that obtaining LI requires that some attention be initially allocated to the preexposed stimulus and then reduced. Implications of the model for understanding attentional dysfunction in schizophrenia are discussed.     

Micro-kinetic modeling of NH3 decomposition on Ni and its application to solid oxide fuel cells

This paper presents a detailed surface reaction mechanism for the decomposition of NH₃ to H₂ and N₂ on a Ni surface. The mechanism is validated for temperatures ranging from 700 to 1500 K and pressures from 5.3 Pa to 100 kPa. The activation energies for various elementary steps are calculated using the unity bond index-quadratic exponential potential (UBI-QEP) method. Sensitivity analysis is carried out to study the influence of various kinetic parameters on reaction rates. The NH₃ decomposition mechanism is used to simulate SOFC button cell operating on NH₃ fuel.     

Confounding of controllability in the triadic design for demonstrating learned helplessness.

The triadic design for producing learned helplessness was analyzed in 2 experiments and found to be logically deficient for defining the theoretical construct of controllability. Two experiments with 120 university students were performed. In Exp I, the 1st group was preexposed to a noxious tone that could be terminated by a button-press. The 2nd and 3rd groups, which were yoked to the 1st, could not escape the tone. A 4th group received no tone preexposures. A 5th group, yoked to the 1st, was instructed to press the button when the tone terminated. Groups 4 and 5, which had no controllability over tone-offset but which did have a 2nd event immediately following the tone, both showed significantly better performance on a subsequent tone-escape task than Group I. Exp II replicated these findings. Data indicate that controllability may be a sufficient but not a necessary condition in the triadic design for preventing subsequent learned helplessness. It follows logically that uncontrollability is not the appropriate designation of the process(es) involved in producing such effects. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search as a function of type of prior experience with target and distractor.

In a visual search task, participants identified the presence of a unique shape against a background of homogeneous distractors. Types of prior experience with the target, the distractor, or both were examined. In 2 experiments, a preexposure (PE) phase was followed by a test phase. The test display consisted of a target that was either target or distractor in PE or novel. Distractors were either targets or distractors in PE or novel. Reaction time was fastest for novel targets with familiar distractors, irrespective of the source of familiarity, and slowest for novel targets with novel distractors. Results are discussed in terms of attentional explanations of latent inhibition (LI) and perceptual learning and of visual search phenomena, such as novel popout. LI, previously attributed only to a deficit in the stimulus preexposed group, may also be due to enhanced performance in the nonpreexposed group. (PsycINFO Database Record (c) 2010 APA, all rights reserved)