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.     

The discrimination of facial expressions by typically developing infants and toddlers and those experiencing early institutional care

Early experience likely plays an important role in the development of the ability to discriminate facial expressions of emotion. We posited that compared to children reared with their biological families (n=72), abandoned children being reared in institutions (n=39) should demonstrate impairments in this ability. The visual paired comparison procedure was utilized to assess the abilities of 13- to 30-month-old children to discriminate among multiple pairs of photographs of facial expressions. Both groups exhibited a normative profile of discrimination, with no group differences evident. Such findings suggest that early institutionalization does not affect the ability of 1- to 3-year-olds to discriminate facial expressions of emotion, at least as inferred by the Visual Paired Comparison Procedure.     

Noise increment detection in children 1 to 3 years of age

Studies using burst comparison procedures to examine age-related changes in intensity discrimination have reported that the ability to discriminate differences in intensity does not reach maturity until late childhood. In the present study, developmental changes in intensity discrimination were examined in 1- to 3-year-old children, using an increment detection paradigm. Children and adults detected increments in a continuous standard presented at three levels ranging from 35 to 55 dB SPL. Adults were also tested at lower levels of the standard in order to permit age comparisons at equivalent sensation levels. Standard stimuli were two-octave bands of noise centered at either 400 or 4000 Hz, and increments were 200 msec in duration. Discrimination performance improved significantly with both age and level of the standard. For all age groups, performance was significantly better for high- than for low-frequency stimuli, but frequency-dependent differences in increment thresholds did not vary reliably with age. Age differences were largest at low levels of the standard. At the highest level (approximately 30 dB nHL), children's difference limens for both low- and high-frequency noise bands were adultlike by 3 years of age. These results suggest that the developmental time course of increment detection is more rapid than that previously reported in burst comparison studies.     

Grasp force control in older adults

Diminished tactile sensibility and impaired hand dexterity have been reported for elderly individuals. Reports that younger adults with severely impaired tactile sensibility use excessive grasp force during routine grasp and manipulation tasks raise the possibility that elderly persons likewise produce large grasp forces that may contribute to impaired dexterity. Impaired pseudomotor functioning also occurs in elderly subjects and may yield a slipperier skin surface that enhances the possibility for excessive grasp force. The present study measured grasp force in 10 elderly and 9 young adult individuals, during grasp and vertical lift of a small object, using a precision (pinch) grip of the thumb and index finger. The slipperiness of the object's gripped surfaces was unexpectedly varied. Skin slipperiness was estimated by also measuring the grasp force at which the object slipped from grasp. The older subjects employed grasp forces that were, on average, twice as large as those of the young subjects, with some producing forces many times greater than the young subjects' average grip force. Grip forces also were significantly more variable across trials in older subjects. This increased variability was not caused simply by the elderly subjects' increased grip force. A portion of the increased force was due to increased skin slipperiness. The grip force that the elderly subjects produced in excess of the slip force (the "margin of safety" against object slippage) was larger than would have been predicted from their skin slipperiness, however. It is suggested that, in part, the excessive grasp forces represent a strategic response to tactile sensibility impairment. Twopoint discrimination limina in the older subjects averaged about four times greater than in the younger subjects. Increased grasp forces in elderly persons may result from other factors, such as increased variability in grip force production. The contributions of excessive grasp forces to impaired dexterity in older persons still need to be addressed experimentally.     

European starlings are capable of discriminating subtle size asymmetries in paired stimuli

Small deviations from bilateral symmetry (fluctuating asymmetries) are cues to fitness differences in some animals. Therefore, researchers have considered whether animals use these small asymmetries as visual cues to determine appropriate behavioral responses (e.g., mate preferences). However, there have been few systematic studies of animals' abilities to visually discriminate such minor asymmetries. If the asymmetries cannot be discriminated, fluctuating asymmetry can not be a visual cue. Here, we report an investigation of European starlings' (Sturnus vulgaris) abilities to discriminate small size asymmetries. We trained starlings, through operant conditioning in a free-flight aviary, to discriminate achromatic, symmetric paired stimuli from size-matched asymmetric stimuli. By starting the learning process with a large asymmetry and progressing through sequential trials of decreasing asymmetry, we elucidated a behavioral limit to asymmetry discrimination. We found that starlings are capable of discriminating a 10% size asymmetry. There was weaker evidence for discrimination of 5% asymmetry but no evidence for signal discrimination at 2.5% size asymmetry. This level of asymmetry discrimination suggests that many size asymmetry cues in nature can be discriminated by birds. At each level of asymmetry discrimination, we also tested whether starlings could generalize their learned symmetry preference to unreinforced novel images. Consistent with previous findings, we found that starlings could generalize their symmetry preferences.     

Schematic concept formation: psychophysical analysis of early reading skill

The relation between the perception of class structure and reading skill was studied within the context of a schematic concept-formation task. Computer generation techniques were utilized to construct visual pattern-classification problems with controlled levels of inter-class pattern similarity of class discrimination difficulty. Children with reading problems were less efficient in their ability to assign patterns to classes than were children without reading problems. It was possible to assess reliably individual subjects' reading skill on the basis of their ability to perform the task.     

Maturation of rapid auditory temporal processing and subsequent nonword repetition performance in children

According to the rapid auditory processing theory, the ability to parse incoming auditory information underpins learning of oral and written language. There is wide variation in this low-level perceptual ability, which appears to follow a protracted developmental course. We studied the development of rapid auditory processing using event-related potentials (ERPs) elicited by tone pairs presented at varying inter-stimulus intervals (25, 50, 100, 200, and 400 ms) in a sample of children (N = 103) aged 7-9 years initially and again at 9-11 years. We also assessed their ability to repeat nonsense words at both time-points. The amount of difference between the ERP to single tones and paired tones (as assessed by the intra-class correlation coefficient, ICC) provided a measure of the brain's capacity to discriminate auditory information delivered at different presentation rates. Results showed that older children showed greater neural discrimination to tone pairs than younger children at rapid presentation rates, although these differences were reduced at slower presentation rates. The ICC at time 1 significantly predicted nonword repetition scores two years later, providing support for the view that rapid auditory temporal processing ability affects oral language development in typically developing children.     

Subjective assessments of firmness: The use of a rating scale

An experiment was carried out to investigate the extent to which an absolute standard for firmness could be held independently of variations occurring within the samples being judged.

Although the method gave good results as a whole, it was found that, when correlating the ratings to the objective measurements, the absolute standards were not held independently of the average firmness of the groups being judged. In practice, if a certain sample was judged, within a “soft” series of samples, it would be rated as being firmer than when it was judged among “firm” samples. Certain differences in the effects of these changes were related to the nature of the subjects' previous experience.

When the results were considered on a relative comparison basis, it was found that a much lower threshold was achieved than had previously been obtained with judgments for springs using paired comparison methods. There were certain trends in the levels of discrimination with time. These trends are discussed.

The strength of grip of the subjects bore some relation to their initial rating values, but apparently was not related to their level of discrimination. Subjects who were able to exert a more constant pressure throughout the test did not seem to be any better at discriminating than were others.

Ratings made for a single sample two months after the main experiment were very similar to those previously given for the same sample.     

Perceptions of personal sex discrimination: the role of belief in a just world and situational ambiguity

The roles of belief in a just world (BJW) and discrimination against ones' group in perceptions of personal discrimination were examined. Female participants (n = 63) were personally discriminated against in a laboratory setting. We manipulated whether the experimenter appeared to discriminate against other participants, which presumably made the presence of personal discrimination less ambiguous, or did not appear to discriminate against others, which presumably made personal discrimination more ambiguous. In the no group discrimination condition, but not in the group discrimination condition, participants' perceptions of being personally discriminated against depended on individual differences in BJW: Women with a strong BJW perceived less personal discrimination than those with a weak BJW. Also, strong BJW women in the group discrimination condition perceived less personal discrimination than strong BJW women in the no group discrimination condition.     

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.     

词频和年级对FOK判断的影响

本实验以识记材料的词频高低和被试年级为自变量对被试元记忆监测的FOK(feeling of knowing)判断进行研究。实验采用Hart提出的RJR(回忆—FOK判断—标准测验 )的经典范式。结果表明 :被试的年级影响FOK判断等级和准确性 ,大学生的FOK判断等级和准确性均高于高一年级学生 ;识记材料词频影响FOK判断等级的高低 ,不影响FOK判断准确性 ,被试对高频词对的FOK判断等级高于对低频词对的FOK判断等级 ,但FOK判断准确性无明显差异。     

Second-order schedules with paired auditory brief stimuli

Pigeons were exposed to multiple second-order schedules of paired and unpaired brief stimuli in which responding on the main key was reinforced according to a fixed-interval thirty-second schedule by a brief stimulus (a tone in the paired schedule) and advancement to the next segment of the second-order schedule. In Experiment 1, a response on the second key was required during the tone in its fourth and final presentation to produce food. Responses during earlier brief stimuli indicated the extent to which the final brief stimulus was discriminated from preceding ones. Responding was comparable during all tones, extending prior findings with visual paired brief stimuli and weakening explanations of subjects' failure to discriminate between brief-stimulus presentations in terms of elicited responding. In Experiment 2 the number of fixed-interval segments comprising the second-order schedules varied from one through eight. Although main-key response rates increased across segments in both experiments, they increased much less sharply with a variable number of segments. These results suggest that the increase in main-key response rates across segments is due primarily to a degree of temporal discrimination not reflected on the second key. Main-key response rates were higher on paired auditory brief-stimulus schedules than on unpaired visual brief-stimulus schedules, especially in Experiment 2, thus further extending findings with visual brief stimuli to second-order schedules with auditory brief stimuli.     

Aging and the perception of speed

Two experiments were conducted to explore the potential effects of aging upon the perception and discrimination of speed. In the first experiment, speed difference thresholds were obtained for younger and older observers for a variety of standard speeds ranging from slow to fast. The second experiment was designed to evaluate the observers' ability to discriminate differences in the speed of moving patterns in the presence of significant amounts of noise (the noise was manipulated by limiting the lifetimes of individual moving stimulus elements). The results of both experiments revealed a significant deterioration in the ability of the older observers to perceive or detect differences in speed. While the presence of noise was found to affect the observers' discrimination performance, it affected both younger and older observers' thresholds in a proportionally equivalent manner-the older observers were no more affected by noise than the younger observers.     

Discrimination of multidimensional geometrical figures by chickens: categorization and pattern-learning

Japanese bantam hens were trained to discriminate between geometrical figures varying along four integral dimensions. Only one dimension predicted food: selections of sharp-cornered figures were reinforced, while selections of rounded figures were not. In experiment 1, hens were subsequently trained to discriminate between nine figure pairs in a simultaneous discrimination task. Because single pairs contained multiple redundant cues, whereas the relevant dimension was obvious only across stimulus pairs, the results revealed effects of both generalization and reversal learning. Accordingly, learning speed was enhanced for later discriminations. Experiment 2 tested the hens’ transfer performance to unknown pairs, following experience of 9 or 18 figure pairs. Four of seven hens showed reliable transfer after experience with 9 figures, but only three showed transfer after experience with 18 figures, indicating lower transfer with higher number of stimulus pairs learned. In experiment 3, hens were trained to discriminate 27 figure pairs. Discrimination ratios further decreased and the groups of pairs differed significantly in their ratios of discrimination. Individual hens’ pecking behaviour was analysed in relation to each dimension of single figures and in relation to relative differences in the levels of dimensions between paired figures. Hens were shown to be oriented towards irrelevant information and more towards relational and configurational than elemental and dimensional aspects. The results are discussed in the biological context of individual recognition in chickens’ dominance hierarchies, in which we suppose that chickens identify individual flock mates by representation of their visual pattern rather than by single characteristics. Received: 18 September 1998 / Accepted after revision: 23 December 1998     

A behavioral frequency discrimination paradigm for use in adult primates

A psychophysical apparatus and procedure that can be used to define the performance and estimate the thresholds of frequency discrimination in adult primates is described. This protocol has been used to train adult owl monkeys to discriminate differences in the frequencies of successively presented sinusoidal tactile stimuli delivered to a restricted skin surface of a single digit, and to train a second set of adult owl monkeys to discriminate. differences in frequencies between paired auditory tonal stimuli. The thresholds estimated with this procedure are comparable to those measured in other primates. The advantages of using this procedure for combined behavioral and physiological studies are discussed.     

Visual discrimination of normal and drug induced behavior in quails (<Emphasis Type="Italic">Coturnix coturnix japonica</Emphasis>)

The ability to discriminate the physical states of others could be an adaptive behavior, especially for social animals. For example, the ability to discriminate illness behavior would be helpful for avoiding spoiled foods. We report on an experiment with Japanese quails testing whether these birds can discriminate the physical states of conspecifics. The quails were trained to discriminate between moving video images of quails injected with psychoactive drugs and those in a normal (not injected) condition. Methamphetamine (stimulant) or ketamine (anesthetic) were used to produce drug-induced behaviors in conspecifics. The former induced hyperactive behavior and the latter hypoactive behavior. The subject quails could learn the discrimination and showed generalization to novel images of the drug-induced behaviors. They did not, however, show discriminative behavior according to the type and dosage of the drugs. Thus, they categorized the behavior not on the basis of degree of activity, but on the basis of abnormality.     

Effects of time-compression on feature and frequency discrimination in aged listeners

This study measured the ability of 16 aged listeners, normal for their age (age range, 63 to 84 yr.) to discriminate phonemic contrasts in sentential stimuli (Subtest 13 of the Carrow-Auditory Visual Abilities Test) presented at 50% time-compression rate. A series of linear regression analyses were performed in which each independent variable was regressed against the continuous variable of age. Over-all performance on the time-compressed task significantly decreased as a function of age. Also discrimination of place of articulation and mid- to high-frequency contrasts was significantly and negatively related to age. In general, such findings suggest that the course of aging continuously imposes degrading effects on speech-processing that are related to discrimination of place feature contrasts.     

Advantage of dichromats over trichromats in discrimination of color-camouflaged stimuli in humans

This study investigated whether 12 participants with color-vision deficiency had superior visual discrimination of color-camouflaged stimuli shown on a computer screen compared with 12 participants with normal trichromatic vision. Participants were asked to distinguish a circular pattern from other patterns in which textural elements differed from the background in orientation and thickness. In one condition, stimuli were single-colored, green or red; in the other condition, stimuli were color camouflaged with a green and red mosaic overlaid onto the pattern. Color-vision deficient participants selected the correct stimuli in the color-camouflaged condition as quickly as they did in the single-colored condition. However, normal color-vision participants took longer to select the correct choice in the color-camouflaged condition than in the single-colored condition. These results suggest that participants with color-vision deficiency may have a superior visual ability to discriminate the color-camouflaged stimuli.     

Great apes’ performance in discriminating weight and achromatic color

Much work has been done on visual discrimination in primates over the past decade. In contrast, very little is known about the relevance of non-visual information in discrimination learning. We investigated weight and achromatic color (color, henceforth) discrimination in bonobos, gorillas and orangutans, using the exchange paradigm in which subjects have to give objects to the experimenter in order to receive a reward. Unlike previous studies, subjects were not trained to lift objects because lifting the objects was an integral part of the exchange procedure. This methodology also allowed us a direct comparison between visual and weight discrimination. We presented 12 subjects (5 bonobos, 2 gorillas and 5 orangutans) with two sets of objects corresponding to two conditions. The objects in the color condition (white/black) differed only in color and those in the weight condition (light/heavy) differed only in weight. Five apes learned to discriminate weight and six to discriminate color. Subjects learned color discrimination faster than weight discrimination. Our results suggest that bonobos and orangutans are sensitive to differences in weight and able to learn discriminating objects that differ in this property.