Preattentive Discrimination Research Articles

Preattentive discrimination of across-category and within-category change in consonant–vowel syllable

Event-related potentials to infrequently presented spoken deviant syllables /pi/ and /po/ among repetitive standard [see text] syllables were recorded in Thai study participants who ignored these stimuli while reading books of their choices. The vowel across-category and within-category changes elicited a change-specific mismatch negativity response. The across-category and within-category change discrimination of vowels in consonant-vowel syllable was also assessed using the low-resolution electromagnetic tomography. The results of low-resolution electromagnetic tomography mismatch negativity generator analysis suggest that the within-category change perception of vowels is analyzed as the change in physical features of the stimuli, thus predominantly activating the right temporal cortex. In contrast, the left temporal cortex is predominantly activated in the across-category change perception of vowels, emphasizing the role of the left hemisphere in speech processing already at a preattentive processing level also in consonant-vowel syllables. The results support the hypothesis that a part of the superior temporal gyrus contains neurons specialized for speech perception.

Early exposure to non-native language alters preattentive vowel discrimination

The present study examined whether early exposure in language immersion would result in better preattentive discrimination of non-native speech sound contrasts. Mismatch negativity (MMN) responses were measured from two groups of Finnish children. The Monolingual group had no prior exposure to other languages than the native one, while the Immersion group consisted of children attending a French immersion program. The subjects were presented with two vowel contrasts in the oddball paradigm: the first pair was phonemic in the native language and the second was a within category pair in Finnish, but phonological in French. The results revealed that the Monolingual group showed a larger response to the native contrast in comparison with the non-native one, whereas both contrasts elicited a similar response in the Immersion group. These results suggest that early exposure to a new language enhances the preattentive discrimination ability reflected in increased MMN amplitude.

The effect of different noise types on the speech and non-speech elicited mismatch negativity

The effect of different types of real-life noise on the central auditory processing of speech and non-speech sounds was evaluated by the means of mismatch negativity and behavioral responses. Subjects (19–34 years old; 6 males, 4 females) were presented, in separate conditions, with either speech or non-speech stimuli of approximately equal complexity in five background conditions: babble noise, industrial noise, traffic noise, wide band noise, and silent condition. Whereas there were no effects of stimuli or noise on the behavioral responses, the MMN results revealed that speech and non-speech sounds are processed differently both in silent and noisy conditions. Speech processing was more affected than non-speech processing in all noise conditions. Moreover, different noise types had a differential effect on the pre-attentive discrimination, as reflected in MMN, on speech and non-speech sounds. Babble and industrial noises dramatically reduced the MMN amplitudes for both stimulus types, while traffic noise affected only speech stimuli.

A visual mechanism tuned to black

Chubb et al. [Journal of the Optical Society of America A 11 (1994) 2350] investigated preattentive discrimination of achromatic textures comprising random mixtures of 17 Weber contrasts ranging linearly from −1 to 1. They showed that only a single mechanism B is used to discriminate between textures whose histograms are equated in mean and in variance. Although they provided a partial characterization of B, their methods did not allow them to measure the sensitivity of B to texture mean and variance. Here, additional measurements are performed to complete the functional characterization of B. The results reveal that B (i) is strongly activated by texture elements of the lowest contrast (near −1), (ii) is slightly activated by texture elements of contrast −0.875, and (iii) barely distinguishes the 15 contrasts ranging from −0.75 all the way up to 1. To reflect the sharpness of its tuning to very dark, sparse elements in a predominantly bright scene, we call B the blackshot mechanism.

Event-Related Potentials (ERPs) – An Up-to-Date Technique in Cognitive Neurosciences

Non-invasively recorded ERPs provide a superb temporal resolution that goes far beyond other up-to-date techniques such as fMRI, PET or TMS. Beyond that, in the auditory modality, the ERP technique offers the unique opportunity to differentiate between attentive behavioral processing and preattentive stimulus detection such as during intraoperative sedation. The current report summarizes a series of cognitive studies that, on the one hand, emphasize time-dependent cognitive functioning in the auditory domain and on the other hand, provide an insight into cognitive functioning where other techniques fail due to logistical reasons [i.e., in cochlear implant (CI) users or during anesthesia]. A first line of evidence comes from studies in awake healthy subjects. It was shown that even a 300µs interaural stimulus delay causes a preattentive cortical ERP that indicates automatic discriminative auditory processing. Moreover, there was evidence for a fast preattentive auditory discrimination within the first stimuli of a complex auditory sequence. In contrast, electrophysiological indicators of attentive stimulus selection processes were delayed by several seconds, thus indicating a dynamic function for attention-dependent auditory processing, whereas preattentive discrimination resembles a preset-like function. Several studies were conducted during anesthesia. It became clear that cortical preattentive auditory discrimination still operates during sevofluran sedation. Beyond that, meaningful auditory novel events (i.e., dog barks) led to a cortical ERP that has formerly been linked to an attentive orienting reaction in awake subjects. Thus, we obtained evidence for a more detailed intraoperative auditory perception than was previously assumed. There is a strong need for objective evaluation in post-implant rehabilitation for CI users, but magnetic interference contraindicates fMRI or TMS. ERPs indicated that CI users preattentively monitor even weak stimulus changes that fail to activate attentively guided selection responses. However, preliminary results indicate that CI users differ from normal controls by means of amplified occipital scalp activation in an auditory discrimination task, thus pointing to a recruitment of the visual cortex for distinctive processing in the auditory modality.

Neural correlates of preattentive face-gender discrimination.

Neural correlates of preattentive face-gender discrimination.

ERP indices of speech processing in bilinguals

The specific aim of this project was to examine perceptual differentiation of the vowel contrast [I-E] by early versus late bilingual Spanish–English speakers, compared to monolingual English speakers. Neither of these phonetic segments occur as phonemes in Spanish while they constitute phonemic contrast in English. For Spanish listeners, these vowels may be heard as variants of the Spanish phonemes [i] and [e], respectively. The formation of perceptual categories may be affected by exposure to two languages in which the phonemic status of phonetic segments differs. In the current study, electrophysiological measures (mismatched negativity—MMN) and behavioral measures (AX discrimination and identification) were employed to examine perception of a nine-step continuum resynthesized from natural tokens. Preliminary results indicate that early bilinguals show somewhat more categorical perception than monolinguals (i.e., sharper identification boundaries) of the nine-step continuum. MMN results, obtained during a task in which subjects were not attending to the auditory input, show clear MMNs for monolinguals for both cross- and within-category pairs. To date, results for early bilinguals show less clear indication of preattentive discrimination. The role of language experience and the relationship between the behavioral performance and the electrophysiological measures will be discussed.

Shifts in the perceived voicing boundary of bilingual listeners

Three groups of listeners, American-English monolinguals, Mexican-Spanish monolinguals, and Mexican-Spanish bilinguals, identified synthetic /ga/–/ka/ syllables varying in VOT. In order to induce a language set in the bilingual listeners, they were asked to produce syllables and phrases in either English or Spanish prior to the identification task. Bilinguals identification of the VOT stimuli varied depending on the language set condition, with the voicing boundary in each case shifting in the direction of values characteristic of monolingual listeners. This effect of language set replicates earlier findings [L. Elman, R. Diehl, and S. E. Buchwald, J. Acoust. Soc. Am. 62, 971–974 (1977)]. Bilinguals velar consonant productions showed a corresponding shift in VOT values across the two language conditions. A Mismatch Negativity paradigm will be used in an attempt to record preattentive discrimination of the language-set-induced phonemic boundary shift in bilingual listeners. [Work supported by the Department of Communication Sciences and Disorders Univ. of Texas–Austin.]

Stability of memory traces for speech sounds in cochlear implant patients

For this study, we examined the perception and production of vowels by postlingually deafened patients with cochlear implant. Four patients and one normally hearing subject produced typical vowel sounds of Finnish by using a speech synthesizer. Also acoustic analyses of the pronounced vowels were made. The first (F1) and the second (F2) formant frequencies were measured. The mismatch negativity (MMN), a cortical cognitive auditory event related potential, was used to measure objectively the patients' preattentive discrimination of a prototypical /i/ sound from deviants differing in the F2 continuum. In the phonetic tests the hyperspace effect was seen also among the patients. The MMN, which reflects the phonetic discrimination ability, could be identified from the patient with the best vowel perception abilities. The phonetic memory traces once developed for vowels seem to remain quite stable even though they have not been activated by vowel information for years.

Brain plasticity in behavioral and neuromagnetic measures: A perceptual training study

The present study investigated brain plasticity in Japanese adults learning the English /l–r/ distinction. Both behavioral and brain (MEG) measures were used. Training was designed to mimic the listening experience of infants who are exposed to the exaggerated acoustic events contained in infant-directed speech (‘‘motherese’’). A multimedia software program incorporated major features conducive to perceptual learning. The program consisted of 12 1-h training sessions. Pre- and post-training measures were collected from nine subjects including two controls. The MEG experiments examined training effects in preattentive discrimination versus categorization conditions. An average improvement of 21.7% was obtained behaviorally. The training effect was significant for all factors of speaker, vowel, and syllabic context. Perceptual learning generalized to three untrained voices. No effects were observed in the two control subjects. Consistent with the behavioral results, the MEG data showed significantly improved mismatch responses in the left hemisphere. Both behavioral and brain data indicated that the learned phonetic boundary in Japanese subjects did not match that of the American listeners. This pattern of results suggests the existence of substantial neural plasticity in adulthood as well as a potential limit. [Work supported by NIH, HFSP, and the Talaris Research Institute.]

Preattentive voice discrimination by the human brain as indexed by the mismatch negativity

The goal of the present study was to determine whether the mismatch negativity (MMN), a component of the auditory event-related potential (ERPs) indexing perceptual difference between any two sounds, could be used as an objective measure of speaker discriminability and similarity/dissimilarity. ERPs were recorded in response to natural speech sounds from subjects watching a silent video. The stimuli consisted of a sequence of repetitive ‘standard’ sounds (the vowel /e/ pronounced by a female voice), which was infrequently interspersed with ‘deviant’ stimuli; the same /e/vowel pronounced by different speakers (one male and three females). Voice intensity and duration were matched between all the voices used. A separate behavioural discrimination task measured the perceptual distance of each deviant voice from the standard voice through pair-wise dissimilarity ratings. The MMN was elicited by all deviant voices. Furthermore, the dissimilarity ratings on the behavioural task paralleled the preattentive discrimination as indexed by the MMN amplitude. These results suggest that the MMN could be used as an objective measure of voice similarity/dissimilarity, and thus could serve objective speaker recognition.

The MMN amplitude increases in hypnosis

The neural mechanisms associated with hypnosis were investigated in a single highly hypnotizable subject by measuring the mismatch negativity (MMN) component of auditory ERP, reflecting the preattentive discrimination of change in stimulus flow, in normal baseline state and under hypnosis. It has been proposed that the frontal inhibition associated with hypnosis can be measured as a decrease in MMN. ERPs were elicited using the passive oddball paradigm with standard and deviant sine tone stimuli of 500 and 553Hz, respectively. The measurement was repeated in five separate sessions. In hypnosis the MMN was significantly larger compared to baseline. The results indicate that hypnosis can give rise to altered information processing in the brain even at a relatively early, i.e. preattentive level and that the larger MMN measured under hypnosis does not support frontal inhibition theory.

Binaural information can converge in abstract memory traces.

Neural representations for abstract features of auditory stimuli were studied by presenting reading subjects with stimulus blocks composed of pairs of two closely spaced tones. There were frequent ascending standard pairs (i.e., the second tone was higher in frequency than the first tone) and occasional descending deviant pairs. Both types of pairs varied randomly over a wide frequency range. In separate blocks, the tones forming a pair were presented either to the same ear or to opposite ears. The deviant pairs elicited the mismatch negativity (MMN) in all conditions, which indicates that the brain can automatically extract and represent an abstract invariant feature (rise or fall) of stimulation above the point of binaural convergence and detect violations against it. Poor behavioral performance in an active discrimination task suggested that conscious discrimination processes can only partially use the outcome of the preattentive discrimination processes reflected by the MMN.

Images, statistics, and textures: implications of triple correlation uniqueness for texture statistics and the Julesz conjecture: comment

The mathematical framework for studies of texture perception is discussed. Textures correspond to statistical ensembles, whereas images are spatially finite samples of a texture. The main ideas underlying the use of visual textures in experimental and theoretical analyses of preattentive vision are summarized, with an emphasis on the distinction between texture ensembles and images. The Julesz conjecture [ Perception2, 391 ( 1973)] is that preattentive discrimination of textures is possible only for textures that have different second-order correlation statistics. Recently Yellot [ J. Opt. Soc. Am. A10, 777 ( 1993)] claimed that the triple correlation uniqueness (TCU) theorem, a mathematical result that every monochromatic image of finite size is uniquely determined (up to translation) by its third-order statistics, makes higher-order variants of the Julesz conjecture trivial. However, the TCU theorem applies to individual images, and not to texture ensembles, and thus is of limited relevance to the study of texture perception.

Preattentive discrimination of relative phase modelled by interacting gabor or by difference-of-gaussian filters

A computer simulation of the human preattentive visual pathway used Gabor and difference-of-Gaussian (DOG) filters to model two-dimensional relative phase discrimination. There is a hierarchy of hexagonally packed levels: (i) an image layer; (ii) an intermediate level of on- and off-centre DOG filters; (iii) a partial set of broadband oriented Gabor-like filters with high-level DOG filters in parallel. Connections between layers use half-wave rectification and a compressive nonlinearity. Local feedback interactions between oriented Gabor filters, together with spatial averaging, allow the model to discriminate both two-dimensional relative phase and orientation differences. There were two separate simulations for die Gabor filters, one with even-symmetric filters and another with odd-symmetric. Textures were formed by superposing three high contrast sine-wave gratings with successive rotations of 60°. Relative phase and global orientation were the varied parameters. Psychophysical rating data for peripheral viewing of texture pairs resemble the results from the even-symmetric simulation, showing discrimination of relative phase and orientation. In contrast, the DOG filters in the model simulate only the relative phase aspects of the data.

Local structure analyzers as determinants of preattentive pattern discrimination

Local structure analyzers as determinants of preattentive pattern discrimination