Electrophysiological evidence for task effects on semantic priming in auditory word processing

Event-related brain potentials (ERPs) associated with semantic relatedness were recorded in two auditory word recognition tasks. In the Memorize task, subjects listened to a list of words in anticipation of a subsequent recognition test. In the Count Nonwords task, subjects silently counted the number of nonwords occurring within a list of words. Within each list, target words were either semantically related or unrelated to the immediately preceding word. As in comparable visual tasks, the amplitude of a negative ERP component (N400) was significantly attenuated when targets were preceded by semantically related primes. This attenuation was greater in the Memorize than in the Count Nonwords task. These data are consistent with the view that the sensitivity of N400 amplitude to semantic relatedness is modulated by task variables that manipulate depth of processing.     

DECISION-MAKING BEHAVIOUR DURING INHALATION OF SUBANAESTHETIC CONCENTRATIONS OF ENFLURANE

The effect of subanaesthetic concentrations of enflurane ondecision-making behaviour in risk situations was assessed usinga signal detection task. The subject heard noise alone (whitenoise) or a signal superimposed on the noise (1000-Hz tone)and had to report what he heard in each trial. Risk situationswere manipulated by changing the monetary reward and penaltyassociated with correct and incorrect responses. Eight malevolunteers participated in this study. It was found that underanaesthetic influence they did not avoid the same risks whichhad been avoided under control conditions. The findings areexplained in terms of influence of the gas on loss of controland lessened responsibility for the result of behaviour. ^*Present address: Aranne Laboratory of Psychophysiology andNeurobehavioral Studies, Department of Neurology, Hadassah UniversityHospital, Jerusalem, Israel.     

EFFECTS OF LOW CONCENTRATIONS OF ENFLURANE ON PROBABILITY LEARNING

The effects of controlled subanaesthetic concentrations of enfluraneon learning behaviour and on ability to change previously developeddecision strategies were studied in 10 male volunteers, usinga probability learning task. Subjects were instructed to predicton each of 200 consecutive trials, whether a left or a rightlight would appear. The appearance of lights was pre-determinedby a set relative frequency unknown to the subject. The relativefrequency was automatically changed at the end of the first100 trials, from 8/10 lights in the left side to 4/10. It wasfound that enflurane at subanaesthetic concentration of 0.25%(end-tidal) slowed the rate of learning, and increased the numberof trials required for readjusting the prediction strategy tothe changed situation. ^*Present address (for correspondence): Aranne Laboratory ofHuman Neuropsychology, Department of Neurology, Hadassah UniversityHospital, Jerusalem, Israel.