Tactile discrimination of gratings: psychophysical and neural correlates in human and monkey.

Human and monkey performance on discriminating tactile gratings revealed comparable cross-species Weber functions. Neural data obtained while monkeys performed discriminations revealed some matching of neural and psychometric functions. Nearly constant firing rate differences occurred at discrimination threshold for unequal groove widths. Firing rate differences of some cells decreased on trials preceding discrimination errors, and thus predicted performance.     

Advertisement-call preferences in diploid-tetraploid treefrogs (Hyla chrysoscelis and Hyla versicolor): implications for mate choice and the evolution of communication systems

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor.     

Gender differences in species recognition and the evolution of asymmetric sexual isolation

Closely related sympatric species are expected to evolve strong species discrimination because of the reinforcement of mate preferences. Fitness costs of heterospecific matings are thought to be higher in females than in males, and females are therefore expected to show stronger species discrimination than males. Here, we investigated gender and species differences in sexual isolation in a sympatric species pair of Calopteryx damselflies. The genus Calopteryx is one of the classic examples of reproductive character displacement in evolutionary biology, with exaggerated interspecific differences in the amount of dark wing coloration when species become sympatric. Experimental manipulation of the extent of dark wing coloration revealed that sexual isolation results from both female and male mate discrimination and that wing melanization functions as a species recognition character. Female choice of conspecific males is entirely based on wing coloration, whereas males in one species also use other species recognition cues in addition to wing color. Stronger species discrimination ability in males is presumably an evolutionary response to an elevated male predation risk caused by conspicuous wing coloration. Gender differences in species discrimination and fitness costs of male courtship can thus shed new light on the evolution of asymmetric sexual isolation and the reinforcement of mate preferences.     

Neural Correlates of Speech Processing in Prelingually Deafened Children and Adolescents with Cochlear Implants

Prelingually deafened children with cochlear implants stand a good chance of developing satisfactory speech performance. Nevertheless, their eventual language performance is highly variable and not fully explainable by the duration of deafness and hearing experience. In this study, two groups of cochlear implant users (CI groups) with very good basic hearing abilities but non-overlapping speech performance (very good or very bad speech performance) were matched according to hearing age and age at implantation. We assessed whether these CI groups differed with regard to their phoneme discrimination ability and auditory sensory memory capacity, as suggested by earlier studies. These functions were measured behaviorally and with the Mismatch Negativity (MMN). Phoneme discrimination ability was comparable in the CI group of good performers and matched healthy controls, which were both better than the bad performers. Source analyses revealed larger MMN activity (155–225 ms) in good than in bad performers, which was generated in the frontal cortex and positively correlated with measures of working memory. For the bad performers, this was followed by an increased activation of left temporal regions from 225 to 250 ms with a focus on the auditory cortex. These results indicate that the two CI groups developed different auditory speech processing strategies and stress the role of phonological functions of auditory sensory memory and the prefrontal cortex in positively developing speech perception and production.     

Gabor filters as texture discriminator

The present paper presents a model for texture discrimination based on Gabor functions. In this model the Gabor power spectrum of the micropatterns corresponding to different textures is calculated. A function that measures the difference between the spectrum of two micropatterns is introduced and its values are correlated with human performance in preattentive detection tasks. In addition, a two stage algorithm for texture segregation is presented. In the first stage the input image is transformed via Gabor filters into a representation image that allows discrimination between features by means of intensity differences. In the second stage the borders between areas of different textures are found using a Laplacian of Gaussian operator. This algorithm is sensitive to energy differences, rotation and spatial frequency and is insensitive to local translation. The model was tested by means of several simulations and was found to be in good correlation with known psychophysical characteristics as texton based texture segregation and micropattern density sensitivity. However, this simple model fails to predict human performance in discrimination tasks based on differences in the density of terminators. In this case human performance is better than expected.     

Matched filtering in motion detection and discrimination

When humans detect and discriminate visual motion, some neural mechanism extracts the motion information that is embedded in the noisy spatio-temporal stimulus. We show that an ideal mechanism in a motion discrimination experiment cross-correlates the received waveform with the signals to be discriminated. If the human visual system uses such a cross-correlator mechanism, discrimination performance should depend on the cross-correlation between the two signals. Manipulations of the signals' cross-correlation using differences in the speed and phase of moving gratings produced the predicted changes in the performance of human observers. The cross-correlator's motion performance improves linearly as contrast increases and human performance is similar. The ideal cross-correlator can be implemented by passing the stimulus through linear spatio-temporal filters matched to the signals. We propose that directionally selective simple cells in the striate cortex serve as matched filters during motion detection and discrimination.     

Preserved Discrimination Performance and Neural Processing during Crossmodal Attention in Aging

In a recent study in younger adults (19-29 year olds) we showed evidence that distributed audiovisual attention resulted in improved discrimination performance for audiovisual stimuli compared to focused visual attention. Here, we extend our findings to healthy older adults (60-90 year olds), showing that performance benefits of distributed audiovisual attention in this population match those of younger adults. Specifically, improved performance was revealed in faster response times for semantically congruent audiovisual stimuli during distributed relative to focused visual attention, without any differences in accuracy. For semantically incongruent stimuli, discrimination accuracy was significantly improved during distributed relative to focused attention. Furthermore, event-related neural processing showed intact crossmodal integration in higher performing older adults similar to younger adults. Thus, there was insufficient evidence to support an age-related deficit in crossmodal attention.     

Chirality of azelastine and flezelastine: Investigation of their enantiomers

The racemic phthalazinone derivatives azelastine and flezelastine were resolved via formation of diastereomeric salts and fractional crystallization thereof. The optical purity of the enantiomers was checked by HPLC. Pharmacological investigations in vitro and in vivo related to antiallergic/antiasthmatic activity revealed some stereospecific differences. However, chiral discrimination could not be observed with regard to overall activity of azelastine and flezelastine. © 1993 Wiley-Liss, Inc.     

Voluntary heart rate deceleration: A critical evaluation

This experiment was designed as a test of the view that the human heart rate (HR) deceleration response can be brought under voluntary control, when some form of exteroceptive feedback is available. Sixteen female volunteers were randomly assigned to two groups. The first group received instructions to decrease their HR plus a continuous negative (failure) binary feedback, while the second group received only the instructions. Each subject was given four sessions of HR deceleration training. Two identical tests were presented, one before and the other after the series of training sessions. These tests were divided into two parts. In the first part, subjects attempted to decrease their HR while undergoing an ischemic arm pain stress. In the second part, subjects performed a 40-trial HR discrimination task. The results indicate that all subjects decrease HR during both rest and voluntary control periods within each training session, but there are no significant group differences, no improvement in HR deceleration control over the four training sessions, and no difference in performance between rest and voluntary control periods. Similarly HR, blood pressure (BP), and the HR×BP product levels during the ischemic stress condition and the HR discrimination performance do not show group differences. It is suggested that the HR deceleration response may not meet the criteria generally applied to the definition of a voluntary response.     

Olfactory discrimination ability and odor structure-activity relationships in honeybees.

Using the training procedure introduced by von Frisch in 1919, we tested the ability of free-flying honeybees to discriminate a conditioning odor from an array of 44 simultaneously presented substances. The stimuli included homologous series of aliphatic alcohols, aldehydes and ketones, isomeric forms of some of these substances, as well as several terpenes and odor mixtures, and thus comprised stimuli of varying degrees of structural similarity to any conditioning odor. We found (i) that the honeybees significantly distinguished between 97.0% of the 1848 odor pairs tested, thus showing an excellent discrimination performance when tested in a free-flying situation with an array of structurally related substances; (ii) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length with all aliphatic substance classes tested; (iii) that both the position and type of a functional group also affected discriminability of odorants in a substance class-specific manner; and (iv) striking similarities in odor structure-activity relationships between honeybees and human and nonhuman primates tested previously on a subset of substances employed here. Our findings demonstrate that the similarities found in the structural organization of the olfactory systems of insects and vertebrates are paralleled by striking similarities in relative discrimination abilities. This strongly suggests that similar mechanisms of odor coding and discrimination may underlie olfaction in vertebrates and insects.     

Interrupting timing in interval production and discrimination: similarities and differences

Interruptions in human timing have been studied in the last few years using temporal production and discrimination tasks. Expecting a break shortened perceived duration in both paradigms but manipulating break duration affected time production only, suggesting that preparatory processes might not take place in time discrimination. In time production, using cues revealed that providing information about the break may modulate the effect of break expectancy. For example, time was perceived as shorter when a break was expected in trials with no breaks, but forewarning participants of the break absence with a cue almost abolished the effect. In the present experiment, a tone was classified as "short" or "long" in a discrimination task. Location and duration of breaks were varied and cues were provided in some trials with no breaks. Results showed an effect of break expectancy: perceived duration shortened with increasing pre-break duration. Reducing expectancy with cues in uninterrupted tones decreased the proportion of "short" responses in long-tone trials, but not in short-tone trials. As in previous discrimination experiments, perceived duration was unaffected by varying break duration. Similarities and differences in results as well as in their interpretation when breaks are used in time production and time discrimination tasks are discussed.     

Extensive Lesions in Rat Insular Cortex Significantly Disrupt Taste Sensitivity to NaCl and KCl and Slow Salt Discrimination Learning

While studies of the gustatory cortex (GC) mostly focus on its role in taste aversion learning and memory, the necessity of GC for other fundamental taste-guided behaviors remains largely untested. Here, rats with either excitotoxic lesions targeting GC (n = 26) or sham lesions (n = 14) were assessed for postsurgical retention of a presurgically LiCl-induced conditioned taste aversion (CTA) to 0.1M sucrose using a brief-access taste generalization test in a gustometer. The same animals were then trained in a two-response operant taste detection task and psychophysically tested for their salt (NaCl or KCl) sensitivity. Next, the rats were trained and tested in a NaCl vs. KCl taste discrimination task with concentrations varied. Rats meeting our histological inclusion criterion had large lesions (resulting in a group averaging 80% damage to GC and involving surrounding regions) and showed impaired postsurgical expression of the presurgical CTA (LiCl-injected, n = 9), demonstrated rightward shifts in the NaCl (0.54 log₁₀ shift) and KCl (0.35 log₁₀ shift) psychometric functions, and displayed retarded salt discrimination acquisition (n = 18), but eventually learned and performed the discrimination comparable to sham-operated animals. Interestingly, the degree of deficit between tasks correlated only modestly, if at all, suggesting that idiosyncratic differences in insular cortex lesion topography were the root of the individual differences in the behavioral effects demonstrated here. This latter finding hints at some degree of interanimal variation in the functional topography of insular cortex. Overall, GC appears to be necessary to maintain normal taste sensitivity to NaCl and KCl and for salt discrimination learning. However, higher salt concentrations can be detected and discriminated by rats with extensive damage to GC suggesting that the other resources of the gustatory system are sufficient to maintain partial competence in these tasks, supporting the view that such basic sensory-discriminative taste functions involve distributed processes among central gustatory structures.     

Human temporal behavior and discrimination-reversal learning

The present study demonstrates that a relationship exists between individual differences in temporal behavior and individual differences in human discrimination-reversal learning behavior. When the results of performance on a time-estimation task employing the method of reproduction are compared with the results of acquisition performance on a complex form of discrimination-reversal learning task is can be demonstrated that underestimation of time is associated with faster learning and overestimation of time is associated with slower learning of the discrimination task. The experimental design was based on the historical fact that the Sechenov-Pavlov and Spence-Hull formulations assigned a primary role in learning to excitation and inhibition as intervening variables between the input of stimulation and output of response. The present study also used the tasks of time estimation and discrimination learning as dependent variables; and the concept that underestimation of time is associated with and underlying predominance of excitatory processes as a hypothetical construct. The conclusion was reached that one of the many theoretical processes which may be used to explain discrimination learning is the concept that acquisition of the correct response may be viewed as a function of the individual rates at which excitatory processes come to be conditioned to a predominance over existing inhibitory processes.     

Odor discrimination and task duration in young and older adults

The effect of task duration on odor discrimination in aging was studied. Twenty-seven young male adults and 24 young female adults between 18 and 30 years of age, and 17 older male adults between 45 and 65 years of age completed an odor discrimination task. The odor discrimination task consisted of two parts of 16 trials each in which, from three bottles consisting of two identical and one aberrant odor, the aberrant odor had to be identified. The two parts were identical except that the aberrant odor was interchanged with the identical odors in the second as compared with the first part. Results revealed a decrease in odor discrimination with age. Moreover, with increased task duration odor discrimination performance decreased considerably in older male adults while it remained unchanged in young male adults. In addition, in young adults a small advantage in females as compared with males was found in the first part of the odor discrimination task, but this effect disappeared with increased task duration. In conclusion, task duration should be taken into consideration as a factor influencing odor discrimination in aging.     

Fast noninertial shifts of attention

It was suggested that some discrimination tasks (e.g. discrimination between the letters T and L) require serial search by scrutinizing each letter (target) with a small aperture of focal attention. Here we examine the effect of intertarget distance on discrimination performance, using two targets. We find reduction in performance at short distances, in agreement with masking studies, but constant performance independent of distance outside this masking region. This constant performance is still lower than expected from masking effects and might reflect attentive process. Sequential presentation of the targets with delays up to 30-40 ms, while reducing available processing time, does not cause reduction in performance, thus supporting the suggestion that discrimination of the two targets is a serial process. The independence of performance on distance suggests fast noninertial shifts of attention.     

Scale morphometry allows discrimination of European sardine Sardina pilchardus and round sardinella Sardinella aurita and among their local populations

Landmark‐based geometric morphometric analysis revealed differences in scale shape between European sardine Sardina pilchardus and round sardinella Sardinella aurita as well as among the local populations of each species. Fish scale measurements from four different areas in the central and eastern Mediterranean Sea showed that the mean scale shape of the two species using landmark data could be differentiated with high certainty. Populations of S. aurita from the central and eastern Mediterranean Sea could be separated reliably (P < 0·001) with an average discrimination rate of 91%, whereas the average discrimination of the S. pilchardus populations was lower (80%), albeit still high.     

Sexually dimorphic responses to neonatal basal forebrain lesions in mice: I. Behavior and neurochemistry

The nucleus basalis magnocellularis (nBM) provides the primary source of cholinergic input to the cortex. Neonatal lesions of the nBM produce transient reductions in cholinergic markers, persistent abnormalities in cortical morphology, and spatial navigation impairments in adult mice. The present study examined sex differences in the effects of an electrolytic nBM lesion on postnatal day 1 (PND 1) in mice on behavior and neurochemistry in adulthood. Mice were lesioned on PND 1 and tested at 8 weeks of age on a battery of behavioral tests including passive avoidance, cued and spatial tasks in the Morris water maze, simple and delayed nonmatch to sample versions of an odor discrimination task, and locomotor activity measurements. Following behavioral testing, mice were sacrificed for either morphological assessment or neurochemical analysis of a cholinergic marker or catecholamines. There were no lesion or sex differences in acquisition or retention of passive avoidance, performance of the odor discrimination tasks, or activity levels. Control mice showed a robust sex difference in performance of the spatial water maze task. The lesion produced a slight cued but more dramatic spatial navigation deficit in the water maze which affected only the male mice. Neurochemical analyses revealed no lesion-induced changes in either choline acetyltransferase activity or levels of norepinephrine or serotonin at the time of testing. The subsequent report shows a sex difference in lesion-induced changes in cortical morphology which suggests that sexually dimorphic cholinergic influences on cortical development are responsible for the behavioral deficits seen in this study. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 582–594, 1998     

Color vision in marmosets and tamarins: behavioral evidence

Here we demonstrate differences in the relative performance of 15 callitrichids tested in a series of color visual discrimination experiments. Munsell color chips were chosen as stimuli based on their use in earlier experiments with human dichromats. We show behavioral evidence for the existence of four distinct kinds of color-vision phenotypes, each of which has slightly different color discrimination abilities. The different phenotypes may offer different advantages. The data are in accordance with the existence of a visual polymorphism in callitrichids.     

False Approximations of the Approximate Number System?

Prior research suggests that the acuity of the approximate number system (ANS) predicts future mathematical abilities. Modelling the development of the ANS might therefore allow monitoring of children's mathematical skills and instigate educational intervention if necessary. A major problem however, is that our knowledge of the development of the ANS is acquired using fundamentally different paradigms, namely detection in infants versus discrimination in children and adults. Here, we question whether such a comparison is justified, by testing the adult ANS with both a discrimination and a detection task. We show that adults perform markedly better in the discrimination compared to the detection task. Moreover, performance on discrimination but not detection, correlated with performance on mathematics. With a second similar experiment, in which the detection task was replaced by a same-different task, we show that the results of experiment 1 cannot be attributed to differences in chance level. As only task instruction differed, the discrimination and the detection task most likely reflect differences at the decisional level. Future studies intending to model the development of the ANS should therefore rely on data derived from a single paradigm for different age groups. The same-different task appears a viable candidate, due to its applicability across age groups.     

Effects of prefeeding, intercomponent-interval food, and extinction on temporal discrimination and pacemaker rate

This experiment investigated the effects of nonpharmacological disruption on temporal discrimination. Pigeons responded on a multiple schedule composed of fixed interval, color-matching, and temporal-discrimination components. The effects of three different disruptors (prefeeding, intercomponent-interval food, and extinction) were assessed. All disruptors decreased response rates during the fixed interval. Prefeeding and intercomponent-interval food had unsystematic effects on response patterning during the fixed interval, whereas extinction increased the relative response rate in the initial portions of the fixed interval. Accuracy of color matching was decreased by prefeeding and was not systematically affected by intercomponent-interval food and extinction. In the temporal-discrimination component, all disruptors flattened the psychophysical functions relating proportion long responses to sample duration. This result indicates a general disruption of temporal discrimination. In addition, parameter estimates derived from the behavioral theory of timing indicated all disruptors decreased pacemaker rate, a result consistent with the predictions of the theory. These results highlight the similarities between disruption of temporal discrimination by pharmacological and nonpharmacological manipulations.