Same-different Discrimination Research Articles

Response bias modulates the speech motor system during syllable discrimination

Recent evidence suggests that the speech motor system may play a significant role in speech perception. Repetitive transcranial magnetic stimulation (TMS) applied to a speech region of premotor cortex impaired syllable identification, while stimulation of motor areas for different articulators selectively facilitated identification of phonemes relying on those articulators. However, in these experiments performance was not corrected for response bias. It is not currently known how response bias modulates activity in these networks. The present functional magnetic resonance imaging experiment was designed to produce specific, measureable changes in response bias in a speech perception task. Minimal consonant-vowel stimulus pairs were presented between volume acquisitions for same-different discrimination. Speech stimuli were embedded in Gaussian noise at the psychophysically determined threshold level. We manipulated bias by changing the ratio of same-to-different trials: 1:3, 1:2, 1:1, 2:1, 3:1. Ratios were blocked by run and subjects were cued to the upcoming ratio at the beginning of each run. The stimuli were physically identical across runs. Response bias (criterion, C) was measured in individual subjects for each ratio condition. Group mean bias varied in the expected direction. We predicted that activation in frontal but not temporal brain regions would co-vary with bias. Group-level regression of bias scores on percent signal change revealed a fronto-parietal network of motor and sensory-motor brain regions that were sensitive to changes in response bias. We identified several pre- and post-central clusters in the left hemisphere that overlap well with TMS targets from the aforementioned studies. Importantly, activity in these regions covaried with response bias even while the perceptual targets remained constant. Thus, previous results suggesting that speech motor cortex participates directly in the perceptual analysis of speech should be called into question.

Emotional processing and executive functioning in children and adults with Tourette's syndrome

Tourette's syndrome (TS) is predominantly a childhood disorder, with many of those who meet diagnostic criteria in childhood experiencing a remission of symptoms in adulthood. This indicates that the influence of TS on cognitive and emotional processing can best be understood by examining performance in both adults and children with TS. The present study examined emotional processing using a battery of face and prosody tasks with increasing levels of difficulty (same-different emotion discrimination, emotion naming, and emotion naming with conflict for prosody only). Experiment 1 compared the performance of children with TS-alone (n = 16) or TS+ADHD (n = 15) to healthy matched control children (n = 27). Compared to healthy control children, no significant group differences were found for those with TS-alone. Children with TS+ADHD showed subtle impairments on the more difficult emotion processing tasks relative to healthy control children, and differences were more pronounced for anger items (voice emotion naming, p < .05; voice emotion naming with conflict, p < .01). Experiment 2 compared the performance of adults with TS-alone (n = 23) to healthy matched controls (n = 21). No significant group differences were found, other than evidence of subtle impairment in the adults with TS-alone on the most complex task, again particularly for anger items (p < .05). Separate measurement of executive skills detected no evidence of impairment in children or adults with TS and little in the way of correlational evidence linking emotion recognition and executive skills. Implications of the findings for our understanding of emotion processing in TS are discussed.

The role of Broca’s area in speech perception: Evidence from aphasia revisited

Motor theories of speech perception have been re-vitalized as a consequence of the discovery of mirror neurons. Some authors have even promoted a strong version of the motor theory, arguing that the motor speech system is critical for perception. Part of the evidence that is cited in favor of this claim is the observation from the early 1980s that individuals with Broca’s aphasia, and therefore inferred damage to Broca’s area, can have deficits in speech sound discrimination. Here we re-examine this issue in 24 patients with radiologically confirmed lesions to Broca’s area and various degrees of associated non-fluent speech production. Patients performed two same-different discrimination tasks involving pairs of CV syllables, one in which both CVs were presented auditorily, and the other in which one syllable was auditorily presented and the other visually presented as an orthographic form; word comprehension was also assessed using word-to-picture matching tasks in both auditory and visual forms. Discrimination performance on the all-auditory task was four standard deviations above chance, as measured using d′, and was unrelated to the degree of non-fluency in the patients’ speech production. Performance on the auditory–visual task, however, was worse than, and not correlated with, the all-auditory task. The auditory–visual task was related to the degree of speech non-fluency. Word comprehension was at ceiling for the auditory version (97% accuracy) and near ceiling for the orthographic version (90% accuracy). We conclude that the motor speech system is not necessary for speech perception as measured both by discrimination and comprehension paradigms, but may play a role in orthographic decoding or in auditory–visual matching of phonological forms.

The dimensional nature of same–different discrimination behavior in pigeons.

We studied the dimensional nature of same-different discrimination behavior in pigeons. Birds first learned to discriminate between simultaneously presented displays of 16 identical items (Same arrays) and 16 nonidentical items (Different arrays), conditional on the color of the background. After discrimination mastery, we tested the birds with Mixture arrays comprising both identical and nonidentical items. Accuracy increased and reaction time decreased as the disparity in entropy (a measure of variability) between the arrays increased. As well, within each entropy disparity level, lower entropy values were more discriminable than higher entropy values. These results accord with a logarithmic relation between entropy and discriminative behavior and, thus, with the idea that the discrimination of Same from Different arrays follows Weber's Law.

Impact of Spectrally Asynchronous Delays on Consonant Voicing Perception

A possible voicing cue used to differentiate voiced and voiceless cognate pairs is envelope onset asynchrony (EOA). EOA is the time between the onsets of two frequency bands of energy (in this study one band was high-pass filtered at 3000 Hz, the other low-pass filtered at 350 Hz). This study assessed the perceptual impact of manipulating EOA on voicing perception of initial stop consonants, and whether normal-hearing and hearing-impaired listeners were sensitive to changes in EOA as a cue for voicing. The purpose of this study was to examine the effect of spectrally asynchronous auditory delay on the perception of voicing associated with initial stop consonants by normal-hearing and hearing-impaired listeners. Prospective experimental study comparing the perceptual differences of manipulating the EOA cues for two groups of listeners. Thirty adults between the ages of 21 and 60 yr completed the study: 17 listeners with normal hearing and 13 listeners with mild-moderate sensorineural hearing loss. The participants listened to voiced and voiceless stop consonants within a consonant-vowel syllable structure. The EOA of each syllable was varied along a continuum, and identification and discrimination tasks were used to determine if the EOA manipulation resulted in categorical shifts in voicing perception. In the identification task the participants identified the consonants as belonging to one of two categories (voiced or voiceless cognate). They also completed a same-different discrimination task with the same set of stimuli. Categorical perception was confirmed with a d-prime sensitivity measure by examining how accurately the results from the identification task predicted the discrimination results. The influence of EOA manipulations on the perception of voicing was determined from shifts in the identification functions and discrimination peaks along the EOA continuum. The two participant groups were compared in order to determine the impact of EOA on voicing perception as a function of syllable and hearing status. Both groups of listeners demonstrated a categorical shift in voicing perception with manipulation of EOA for some of the syllables used in this study. That is, as the temporal onset asynchrony between low- and high-frequency bands of speech was manipulated, the listeners' perception of consonant voicing changed between voiced and voiceless categories. No significant differences were found between listeners with normal hearing and listeners with hearing loss as a result of the EOA manipulation. The results of this study suggested that both normal-hearing and hearing-impaired listeners likely use spectrally asynchronous delays found in natural speech as a cue for voicing distinctions. While delays in modern hearing aids are less than those used in this study, possible implications are that additional asynchronous delays from digital signal processing or open-fitting amplification schemes might cause listeners with hearing loss to misperceive voicing cues.

Evidence for a pre-match 'mental translation' on a form-matching task

PURPOSE AND APPROACH. The aim was to explore whether there is a pre-match ‘mental translation’, analogous to ‘mental rotation’ and ‘mental scaling’, on a Same-Different simultaneous form-matching task. The basic approach was to vary the environmental separation of the forms, while holding constant everything else that might affect reaction time. METHOD. On a Same-Different task, subjects were presented with two forms flanking a fixation triangle, all shown in the same depth-plane. Distance (simulated) to the forms was varied. Viewing was in stereo. Total visual angle spanned by the centers of the bases of the two forms, in each eye, was held (essentially, effectively) constant as distance to the forms (and so environmental separation) varied. The forms and fixation triangle were shown resting on a bar that spanned a textured enclosure; the top of the bar crossed at eye-level and the bar was anchored to the floor of the enclosure by struts. The top half of the back of the enclosure was open, with the forms silhouetted against a blank field. So: form edge-information and gaze angle were both held constant as distance to the forms (and so environmental separation) varied, and there was no backing surface. In Experiment I, the forms were shown for 400msc; in Experiment II, the forms were shown for 300msc, and the Same-Different discrimination was made slightly easier. RESULTS AND CONCLUSION. In Experiment I, reaction time rose with increases in environmental separation (n = 34, p < .01, R-squared = .9295; Same trials). Results for the 16 subjects run so far in Experiment II also indicate a rise in reaction time with increases in environmental separation (p = .029; Same trials). In both cases, the slopes suggest a fast process. In sum, the results are evidence that comparisons of the forms were preceded by a fast ‘mental translation’, analogous to ‘mental rotation’ and ‘mental scaling’, with the locations of the forms coded in a non-retinal frame of reference.

Conditional same-different discrimination by pigeons: Acquisition and generalization to novel and few-item displays.

The authors explored whether pigeons can learn to discriminate simultaneously presented arrays of 16 identical (Same) visual items from arrays of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background. In one experiment, pigeons rapidly learned this task and, after training with arrays created from a 72-icon set, they exhibited nearly perfect transfer to novel testing arrays. In a second experiment, pigeons' accuracy to 24-, 20-, 12-, and 8-icon arrays during later testing remained as high as accuracy to training arrays; although accuracy declined with 4- and 2-icon arrays, it was still significantly above chance. In both experiments, pigeons' choice reaction time scores nicely complemented their choice accuracy scores. These results suggest that the conditional discrimination procedure is well suited to disclose same-different discrimination in pigeons and to elucidate the interaction between perception and abstraction in conceptual learning.

Same–different discrimination: The keel and backbone of thought and reasoning.

Discriminating same from different collections of items is central to human thought and reasoning. Recent comparative research suggests that same-different discrimination behavior is not uniquely human, does not require human language, is based on the variability of the collection of items, obeys fundamental psychophysical laws, and may be captured by quantitative models of the stimulus collection. The comparative study of same-different discrimination behavior sheds fresh light on the mechanisms and functions of abstract conceptualization. This study also has prompted the development of a theory-the Finding Differences Model-that successfully explains a wealth of findings in the comparative psychology of same-different discrimination behavior.

Effects of stimulus size and spatial organization on pigeons’ conditional same–different discrimination

In two experiments, we explored the effects of varying the size and the spatial organization of the stimuli in multi-item arrays on pigeons' same-different discrimination behavior. The birds had previously learned to discriminate a simultaneously presented array of 16 identical (Same) visual items from an array of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background (Castro et al., in press). In Experiment 1, we trained pigeons with 7-item arrays and then tested them with arrays containing the same item, but in a variety of sizes. In Experiment 2, we tested the birds with the items grouped in novel locations: the top, the bottom, the left, or the right portions of the display area, which generated different vertical and horizontal alignments. Accuracy scores revealed virtually perfect stimulus generalization across various item sizes and spatial organizations. Reaction times revealed that the birds perceived different sizes of a single icon as the same stimulus (Experiment 1) and that the birds processed vertical arrangements faster than horizontal arrangements (Experiment 2). These results suggest that the pigeons noticed both physical and spatial changes in the stimuli (as shown by their reaction times), but that these changes did not disrupt the birds' discriminating the sameness or differentness of the multi-item arrays (as shown by their accuracy scores).

Affective same-different discrimination tests for assessing consumer discriminability between milks with subtle differences

Affective and analytical same-different discrimination tests for assessing the ability of consumers to discriminate between milks with subtle differences were designed by applying familiarization procedures to induce an affective/synthetic and analytical/synthetic perceptual strategy. The tests were then administered to 100 milk consumers and compared. In both same-different discriminations, consumers adopted a cognitive decision rule that used a β-strategy rather than a τ-strategy. Discrimination tests employing an affective/synthetic perceptual approach (which is the normal consumer perceptual process) resulted in higher discriminability than tests that employed an analytical/synthetic approach. Inter-individual differences in the consumer criteria (boundaries) used for same-different ratings were studied by examining the response distributions over the given response categories for the same pairs. According to the similarity of such response distributions, two different consumer segments were classified and their group discriminabilities differed significantly, with only the more sensitive group showing interactions between the affective/hedonic state and perceptual discriminability.

Spatiotemporal Interactions in Retinal Prosthesis Subjects

Vision loss due to retinitis pigmentosa affects an estimated 15 million people worldwide. Through collaboration between Second Sight Medical Products, Inc., and the Doheny Eye Institute, six blind human subjects underwent implantation with epiretinal 4 x 4 electrode arrays designed to directly stimulate the remaining cells of the retina, with the goal of restoring functional vision by applying spatiotemporal patterns of stimulation. To better understand spatiotemporal interactions between electrodes during synchronous and asynchronous stimulation, the authors investigated how percepts changed as a function of pulse timing across the electrodes. Pulse trains (20, 40, 80, and 160 Hz) were presented on groups of electrodes with 800, 1600, or 2400 microm center-to-center separation. Stimulation was either synchronous (pulses were presented simultaneously across electrodes) or asynchronous (pulses were phase shifted). Using a same-different discrimination task, the authors were able to evaluate how the perceptual quality of the stimuli changed as a function of phase shifts across multiple electrodes. Even after controlling for electric field interactions, subjects could discriminate between spatiotemporal pulse train patterns based on differences of phase across electrodes as small as 3 ms. These findings suggest that the quality of the percept is affected not only by electric field interactions but also by spatiotemporal interactions at the neural level. During multielectrode stimulation, interactions between electrodes have a significant influence on the quality of the percept. Understanding how these spatiotemporal interactions at the neural level influence percepts during multielectrode stimulation is fundamental to the successful design of a retinal prosthesis.

Glyconutrients and Perception, Cognition, and Memory

Neuropsychological tests were administered to 62 college students to assess the influence of glyconutrients on perception, cognition and memory in two randomized, double-blind, placebo-controlled, counterbalanced studies. Participants were given both a glyconutritional supplement and a control substance prior to testing. In Exp. 1. a Same-Different visual discrimination task, Raven's Standard Progressive Matrices, and the Stroop test were administered. In Exp. 2, simple and complex working-memory capacity were measured. Participants receiving the supplement performed significantly more accurately on the visual discrimination task and the first session of the simple working-memory test.

Generalized auditory same-different discrimination by pigeons.

Three pigeons were trained in a successive same/different (S/D) procedure using compound auditory stimuli (pitch/timbre combinations). Using a go/no-go procedure, pigeons successfully learned to discriminate between sequences of either all same (AAAA...or BBBB...) or all different (ABCD...) sequences consisting of 12 sounds. Both pitch and timbre were subsequently established as controlling dimensions. Transfer tests with novel stimuli revealed a generalized basis for the discrimination (novel pitch/timbre combinations, novel pitches, novel instruments, and complex natural & man-made sounds). These results indicate for the first time that pigeons can learn generalized same/different discriminations in a nondominant modality. When combined with earlier visual results, they support a qualitative similarity among birds and primates in their capacity to judge this type of fundamental stimulus relation across different modalities.

On the ability to discriminate Gaussian-noise tokens or random tone-burst complexes

This study investigated factors that influence a listeners' ability to discriminate Gaussian-noise stimuli in a same-different discrimination paradigm. The first experiment showed that discrimination ability increased with bandwidth for noise durations up to 100 ms. Duration had a nonmonotonic influence on performance, with a decrease in discriminability for stimuli longer than 40 ms. Further experiments investigated the cause for this performance decrease. They showed that discriminability could be improved when using frozen-noise tokens and by instructing listeners to focus on the stimulus endings. A final experiment, using a stimulus consisting of 5 ms Hanning-windowed tone-bursts randomly distributed over time, investigated whether stimulus duration and amount of information differently affect the processing capacity of the auditory system. Results showed that the number of degrees of freedom in the stimulus, not its duration, predominantly influenced the ability to discriminate. Overall, the results suggest that the discrimination performance for acoustic stimuli depends strongly on the amount of information per critical band and the capacity to process this information. This capacity seems to be limited in the temporal dimension, while extending the signal over more auditory filters does have a positive effect on performance.

Effects of two training procedures in cross-language perception of tones

This study evaluated two perceptual training procedures that might be used to increase native English (NE) and native Chinese (NC) listeners’ ability to discriminate the mid- vs. low-tone contrast in Thai under two inter-stimulus-interval (ISI) conditions (500 and 1500 ms). Participants received training using either a two-alternative forced-choice identification (ID) procedure or a categorial same/different discrimination (SD) procedure. The results obtained indicated that (a) NC listeners outperformed NE listeners both before and after training under both ISI conditions; (b) before training, NC listeners’ discrimination was better under the longer ISI while NE listeners’ performance was comparable across the two ISIs, but no ISI difference was observed for either group of listeners after training; (c) both NE and NC listeners’ performances significantly improved after training, but the improvement was significantly greater among NE listeners under both ISI conditions, and (d), the amount of improvement was comparable across the two training procedures and across the two ISI conditions. These results suggest that both ID and SD training procedures were equally effective in improving NE and NC listeners’ discrimination of the mid- vs. low-tone contrast in Thai and that prior experience with a tone language may prove advantageous in learning another tone language.

Acoustic and Perceptual Similarities Between English and Korean Sibilants

Abstract. Foreign accent has been assumed to be closely related to the degree of articulatory, acoustic and perceptual similarity between L1 and L2 sounds. This study examined cross-language acoustic and perceptual similarities between Korean and English sibilant fricatives: Korean [—tense] /s/ and [+tense] /s*/ vs. English alveolar /s/ and palato-alveolar /∫/. To determine acoustic similarity, two parameters were measured: duration and spectral peak frequency. A Same-Different (AX) discrimination task investigated listeners' perceived similarity judgments between pairs of sibilants. In most cases, the acoustic characterizations led to correct predictions about differences in listeners' perceptions. However, results showed several disparities between acoustic similarity and perceived similarity. These cases necessarily involve acoustic dimensions other than the two measured here; probable candidates are voice quality on a following vowel, and lip rounding, with its spectral lowering effects. Cases of mismatch between acoustic and perceptual characterizations are fruitful areas for examining additional acoustic characteristics that may be responsible for listeners' ability to distinguish sounds. Acoustic and perceptual characterizations in tandem provide the best method of establishing areas of difference between the sounds of different languages, and in turn of establishing ways to teach L2 sounds to learners.

Maintaining readiness for mental rotation interferes with perceptual processes in children but with response selection in adults

Previous work revealed that mental rotation is not purely inserted into a same-different discrimination task. Instead, response time (RT) is slowed to upright stimuli in blocks containing rotated stimuli compared to RT to the same upright stimuli in pure upright blocks. This interference effect is a result of maintaining readiness for mental rotation. In two experiments we investigated previous evidence that these costs depend upon distinct sub-processes for children and for adults. In Experiment 1, the maintaining costs turned out to be independent of the visual quality of the stimulus for adults but not so for children. Experiment 2 revealed that the maintaining costs were greatly reduced for adults when they performed mental rotation as a go-no-go task, but not so for children. Taken together, both experiments provide evidence that whereas perceptual processes seem to be important for school-age children to maintain readiness for mental rotation, response selection is relevant for adults.

Short-term item memory in successive same–different discriminations

Pigeons were tested in a successive same-different (S/D) discrimination procedure to examine the short-term memory for individual items in sequences of different or identical pictures. Item-by-item analyses of pecking behavior within single trials revealed this S/D discrimination emerged at the earliest possible point in the sequence--the presentation of the second item. Further, by comparing peck rates at points where different types of sequences diverged (e.g. ABA versus ABC), we determined that the pigeons remembered the first item for at least 4-8s and across one to two intervening items. These results indicate that this S/D discrimination was controlled by relational comparisons of pictorial content across memories of specific items, rather than the detection of low-level perceptual "transients" between items. A second experiment supported this conclusion by showing increased discrimination with longer first item viewing times, consistent with encoding of details about individual pictures. These findings further support a qualitative similarity among birds and primates in possessing a general capacity to judge certain types of stimulus relations, such as stimulus identity and difference. Implications for the temporal continuity of experience in animals are also considered.

Auditory Processing Deficits in Dyslexia: Task or Stimulus Related?

The nature of the fundamental deficit underlying reading disability is the subject of a long-standing debate. We previously found that dyslexics with additional learning difficulties (D-LDs) perform poorly in simple auditory tasks. We now tried to determine whether these deficits relate to stimulus or task complexity. We found that the degree of impairment was dependent on task rather than stimulus complexity. D-LDs could adequately detect and identify mild frequency changes in simple pure tones and minimal phonemic changes in complex speech sounds when task required only simple same-different discriminations. However, when task required the identification of the direction of frequency change or the ordinal position of a repeated tonal or speech stimulus, D-LDs' performance substantially deteriorated. This behavioral pattern suggests that D-LDs suffer from a similar type of deficits when processing speech and nonspeech sounds. In both cases, the extent of difficulties is determined by the structure of the task rather than by stimulus composition or complexity.

Not all same-different discriminations are created equal: Evidence contrary to a unidimensional account of same-different learning

In Experiment 1, we trained four pigeons to concurrently discriminate displays of 16 same icons (16S) from displays of 16 different icons (16D) as well as between displays of same icons (16S) from displays that contained 15 same icons and one different icon (15S:1D). The birds rapidly learned to discriminate 16S vs. 16D displays, but they failed to learn to discriminate 16S vs. 15S:1D displays. In Experiment 2, the same pigeons acquired the 16S vs. 15S:1D task after being required to locate and peck at the odd-item in the 15S:1D displays. Acquisition of the 16S vs. 15S:1D task had little effect on discriminative performance in the concurrent 16S:16D task, suggesting that a unidimensional entropy explanation for mastery of these two same-different tasks is not viable. During testing, the birds transferred discriminative performance in both tasks to displays composed of different visual stimuli. Such concurrent discrimination learning, performance, and transfer suggest that pigeons are flexible in the way they process the displays seen in these two same-different tasks.