Effect of mouth opening on bite-force discrimination

The purpose of this study was to determine whether different extents of mouth opening affect normal subjects' (N = 24; 12 women, 12 men) ability to discriminate differences in their interincisor bite force. Three mouth openings were selected including 50, 70, and 90 percent of maximum opening for each subject. Bite force was measured using a specially designed strain gauge scale which permitted subjects to monitor visually when their biting force equalled a preset resistance. Resistance forces of 500 and 1000 gm. were selected as standards. The procedure involved the use of a modified method of constant stimuli in which each subject was presented with a series of paired resistance settings, one at a time--the first resistance setting being the standard and the second resistance was the comparator. This paired-comparisons procedure was continued until the subjects' difference limen (DL) value (the threshold of discrimination between two forces) could be established. An analysis of variance yielded no significant differences in subjects' ability to discriminate bite force as a function of mouth opening.     

Phonetic discrimination ability of a native vowel contrast in preterm infants

Preterm birth is considered a risk factor for cognitive and linguistic development; however, research focusing on the comparison between preterm and full term infants' early abilities in speech perception is still scarce. In this study, the ability to perceive and discriminate a native vowel contrast by a sample of preterm infants at 4 and 8 months of age (corrected for gestation) has been analyzed using the familiarization-preference procedure and complex stimuli (CV.CV, multispeakers). Results reveal differences at 4 months of age between pre-term and control groups; only the latter successfully categorize and react to the vowel change. By 8 months of age, preterm infants are able to solve the task. A positive correlation was observed between duration of attention (visual fixation measures) and a number of neonatal risk factors. Results show the effects of preterm birth on the processing of complex stimuli and suggest the need to further explore the connection between early speech perception capacities and language development in this at-risk population.     

Contrast discrimination in human infants

The ability to detect differences in spatial contrast is crucial to object recognition and identification. This ability is generally examined by measuring the contrast discrimination function. This function represents, for a variety of conditions, the smallest contrast difference required to discriminate otherwise identical patterns. We examined human infants' ability to discriminate patterns on the basis of differences in spatial contrast. The forced-choice preferential looking procedure was used to estimate contrast increment thresholds at a number of background contrasts. The Weber fractions of 6- and 12-week-old infants were about 1 log unit higher than adult values for background contrasts ranging from 0.14 to 0.55. Furthermore, the slopes of infants' discrimination functions were much shallower than those of adults. These age differences in contrast discrimination imply certain changes in the neural mechanisms that underlie contrast encoding. They also aid our understanding of the anomalies observed in early pattern vision.     

Effect of prior Pavlovian discrimination training upon learning an operant discrimination

The effect of Pavlovian discrimination training with two stimuli upon subsequent learning of an operant discrimination involving those stimuli was studied. After preliminary lever press training, the lever was removed and thirsty rats received noncontingent pairings between S₁ (a tone or a clicker) and water reinforcements, whereas S₂ (a clicker or a tone) occurred always without reinforcement. This procedure presumably established S₁ as a positive CS for respondent behavior, whereas S₂ was established as an inhibitory CS. Following this training, the lever was reintroduced and the rats were trained on an operant (lever pressing) discrimination involving S₁ and S₂. For the Consistent Ss, S₁ was the S^D and S₂ the S^Δ in the operant discrimination; for the Reversed Ss, S₂ served as S^D and S₁ as S^Δ. The Consistent Ss learned the operant discrimination significantly faster than did the Reversed Ss. The result emphasizes the importance of respondents, conditioned to S^D and S^Δ, which modulate operant performance to these stimuli.     

Mental ability and the effect of pattern violation discrimination on P300 and mismatch negativity

The relation between mental ability and the ability to detect auditory pattern violations was examined using event-related potential measures, specifically P300 and mismatch negativity (MMN). Thirty female volunteers were presented with a two tone alternating pattern containing infrequent repetition violations in passive (ignore) then active response conditions. Task difficulty was manipulated by varying the tonal separation between the two constituent tones of the pattern, i.e., separated by 1 or 6 semitones. In the active pattern violation discrimination condition, the greater difficulty of the 1 semitone discrimination was confirmed by reduced accuracy, more false positive responses, longer response times, and greater variability in response times than for 6 semitones. Higher ability (HA) was associated with greater response accuracy, shorter response times, less variable response times, shorter P300 latency, and greater P300 amplitude, predominantly in the more difficult 1 semitone condition. These effects are indicative of greater facility and speed of discriminating pattern violations for HA. In the passive condition, HA was associated with larger MMN amplitude to the deviant tones in both semitone conditions. The MMN effect indicates that the facility in pattern violation discrimination develops prior to consciousness, and cannot be attributed to conscious processes like focussed attention.     

The direction of masked auditory category priming correlates with participants' prime discrimination ability

Semantic priming refers to the phenomenon that participants typically respond faster to targets following semantically related primes as compared to semantically unrelated primes. In contrast, Wentura and Frings (2005) found a negatively signed priming effect (i.e., faster responses to semantically unrelated as compared to semantically related targets) when they used (a) a special masking technique for the primes and (b) categorically related prime-target-pairs (e.g., fruit-apple). The negatively signed priming effect was most pronounced for participants with random prime discrimination performance, whereas participants with high prime discrimination performance showed a positive effect. In the present study we analyzed the after-effects of masked category primes in audition. A comparable pattern of results as in the visual modality emerged: The poorer the individual prime discrimination, the more negative is the semantic priming effect. This result is interpreted as evidence for a common mechanism causing the semantic priming effect in vision as well as in audition instead of a perceptual mechanism only working in the visual domain.     

Differential effects of instructions and consequences on human conditional discrimination performance

Two studies evaluated the differential behavioral effects of instructions and feedback in matching-to-sample procedures. In Experiment 1, 20 college students received true or false instructions and trial-by-trial or delayed feedback in three phases. In a fourth, final phase the instructions remained the same, but feedback changed from trial-by-trial to delayed, or from delayed to trial-by-trial. In Experiment 2, half of another 20 participants received true instructions during three phases, followed by false instruction in a fourth phase; the other half of the participants received false instructions during three phases, followed by true instructions in the fourth phase. Feedback sequences were as in Experiment 1. The results of both experiments revealed historical effects of instructions and feedback. Most participants demonstrated strong instructional control, overriding the control by contingencies. These results suggest that the present procedure offers optimal possibilities to make the differential effects of instructions and feedback on human behavior clearly identifiable when conditional discrimination tasks are used.