Levels Of Stimulus Complexity Research Articles

Speech Processing in Autism Spectrum Disorder: An Integrative Review of Auditory Neurophysiology Findings.

Purpose Investigations into the nature of communication disorders in autistic individuals increasingly evaluate neural responses to speech stimuli. This integrative review aimed to consolidate the available data related to speech and language processing across levels of stimulus complexity (from single speech sounds to sentences) and to relate it to the current theories of autism. Method An electronic database search identified peer-reviewed articles using event-related potentials or magnetoencephalography to investigate auditory processing from single speech sounds to sentences in autistic children and adults varying in language and cognitive abilities. Results Atypical neural responses in autistic persons became more prominent with increasing stimulus and task complexity. Compared with their typically developing peers, autistic individuals demonstrated mostly intact sensory responses to single speech sounds, diminished spontaneous attentional orienting to spoken stimuli, specific difficulties with categorical speech sound discrimination, and reduced processing of semantic content. Atypical neural responses were more often observed in younger autistic participants and in those with concomitant language disorders. Conclusions The observed differences in neural responses to speech stimuli suggest that communication difficulties in autistic individuals are more consistent with the reduced social interest than the auditory dysfunction explanation. Current limitations and future directions for research are also discussed.

From modulated noise to natural speech: The effect of stimulus parameters on the envelope following response

Envelope following responses (EFRs) can be evoked by a wide range of auditory stimuli, but for many stimulus parameters the effect on EFR strength is not fully understood. This complicates the comparison of earlier studies and the design of new studies. Furthermore, the most optimal stimulus parameters are unknown. To help resolve this issue, we investigated the effects of four important stimulus parameters and their interactions on the EFR. Responses were measured in 16 normal hearing subjects evoked by stimuli with four levels of stimulus complexity (amplitude modulated noise, artificial vowels, natural vowels and vowel-consonant-vowel combinations), three fundamental frequencies (105 Hz, 185 Hz and 245 Hz), three fundamental frequency contours (upward sweeping, downward sweeping and flat) and three vowel identities (Flemish /a:/, /u:/, and /i:/). We found that EFRs evoked by artificial vowels were on average 4–6 dB SNR larger than responses evoked by the other stimulus complexities, probably because of (unnaturally) strong higher harmonics. Moreover, response amplitude decreased with fundamental frequency but response SNR remained largely unaffected. Thirdly, fundamental frequency variation within the stimulus did not impact EFR strength, but only when rate of change remained low (e.g. not the case for sweeping natural vowels). Finally, the vowel /i:/ appeared to evoke larger response amplitudes compared to /a:/ and /u:/, but analysis power was too small to confirm this statistically. Vowel-dependent differences in response strength have been suggested to stem from destructive interference between response components. We show how a model of the auditory periphery can simulate these interference patterns and predict response strength. Altogether, the results of this study can guide stimulus choice for future EFR research and practical applications.

Perceptual training enhances temporal acuity for multisensory speech

The temporal relationship between auditory and visual cues is a fundamental feature in the determination of whether these signals will be integrated. The window of perceived simultaneity (TBW) is a construct that describes the epoch of time during which asynchronous auditory and visual stimuli are likely to be perceptually bound. Recently, a number of studies have demonstrated the capacity for perceptual training to enhance temporal acuity for audiovisual stimuli (i.e., narrow the TBW). These studies, however, have only examined multisensory perceptual learning that develops in response to feedback that is provided when making judgments on simple, low-level audiovisual stimuli (i.e., flashes and beeps). Here we sought to determine if perceptual training was capable of altering temporal acuity for audiovisual speech. Furthermore, we also explored whether perceptual training with simple or complex audiovisual stimuli generalized across levels of stimulus complexity. Using a simultaneity judgment (SJ) task, we measured individuals’ temporal acuity (as estimated by the TBW) prior to, immediately following, and one week after four consecutive days of perceptual training. We report that temporal acuity for audiovisual speech stimuli is enhanced following perceptual training using speech stimuli. Additionally, we find that changes in temporal acuity following perceptual training do not generalize across the levels of stimulus complexity in this study. Overall, the results suggest that perceptual training is capable of enhancing temporal acuity for audiovisual speech in adults, and that the dynamics of the changes in temporal acuity following perceptual training differ between simple audiovisual stimuli and more complex audiovisual speech stimuli.

The Role of Olfactory Cues for the Search Behavior of a Specialist and Generalist Butterfly

Searching for resources is often a challenging task, especially for small organisms such as insects. Complex stimuli have to be extracted from the environment and translated into a relevant behavioral output. A first step in this process is to investigate the relative roles of the different senses during search for various resources. While the role of olfaction is well documented in nocturnal moths, the olfactory abilities of the closely related diurnal butterflies are poorly explored. Here we investigated how olfactory information is used in the search for host plants and asked if these abilities varied with levels of stimulus complexity. Thus, we tested two nymphalid butterfly species with divergent host plant range in a two-choice olfactometer testing different combinations of host and non-host plants. The experiments show both the monophagous Aglais urticae and the polyphagous Polygonia c-album could navigate towards an odor source, but this ability varied with context. While mated females exhibited a preference for their host plant, unmated females of both species did not show a preference for host plant cues. Furthermore, both species showed inabilities to make fine-tuned decisions between hosts. We conclude that olfactory cues are important for butterflies to navigate towards targets. We argue that there are limitations on how much information can be extracted from host volatiles. These results are discussed in the light of neural processing limitations and degree of host plant specialization, suggesting the necessity of other sensory modalities to sharpen the decision process and facilitate the final oviposition event.

Dissociating Cortical Activity during Processing of Native and Non-Native Audiovisual Speech from Early to Late Infancy.

Initially, infants are capable of discriminating phonetic contrasts across the world’s languages. Starting between seven and ten months of age, they gradually lose this ability through a process of perceptual narrowing. Although traditionally investigated with isolated speech sounds, such narrowing occurs in a variety of perceptual domains (e.g., faces, visual speech). Thus far, tracking the developmental trajectory of this tuning process has been focused primarily on auditory speech alone, and generally using isolated sounds. But infants learn from speech produced by people talking to them, meaning they learn from a complex audiovisual signal. Here, we use near-infrared spectroscopy to measure blood concentration changes in the bilateral temporal cortices of infants in three different age groups: 3-to-6 months, 7-to-10 months, and 11-to-14-months. Critically, all three groups of infants were tested with continuous audiovisual speech in both their native and another, unfamiliar language. We found that at each age range, infants showed different patterns of cortical activity in response to the native and non-native stimuli. Infants in the youngest group showed bilateral cortical activity that was greater overall in response to non-native relative to native speech; the oldest group showed left lateralized activity in response to native relative to non-native speech. These results highlight perceptual tuning as a dynamic process that happens across modalities and at different levels of stimulus complexity.

PC.21 Eye-tracking methodology for the assessment of social function in infancy

BackgroundEye-tracking has provided new insights into the development of infant cognition and is currently being explored as a potential way to identify early biomarkers of later difficulty. We aimed to...

94. ERP modulation in patients with disorders of consciousness

The limited evidence and inconsistency of purposeful behaviors in patients in a minimally conscious state (MCS) asks for objective electrophysiological marker of the level of consciousness. Here, a comparison between event-related potentials (ERPs) was investigated using different level of stimulus complexity. ERPs were recorded in 17 patients, 11 of which in vegetative state (VS), 6 in MCS, and 10 controls. Three oddball paradigms with different level of complexity were applied: sine tones, the subject’s own name vs. sine tones and other first names. Latencies and amplitudes of N1 and P3 waves were compared using a semi-automated peak detection algorithm. Cortical responses were found in all MCS patients, and in 6 of 11 patients in VS. Healthy controls and MCS patients showed a progressive increase of P3 latency in relation to the level of stimulus complexity. No modulation of P3 latency was observed in the vegetative patients. These results suggest that the modulation of P3 latency related to stimulus complexity may represent an objective index of higher-order processing integration that predicts the recovery of consciousness from VS to MCS when clinical manifestations are inconsistent. P3 latency modulation may help differentiate between different states of consciousness.

Dogs Cannot Bark: Event-Related Brain Responses to True and False Negated Statements as Indicators of Higher-Order Conscious Processing

The present study investigated event-related brain potentials elicited by true and false negated statements to evaluate if discrimination of the truth value of negated information relies on conscious processing and requires higher-order cognitive processing in healthy subjects across different levels of stimulus complexity. The stimulus material consisted of true and false negated sentences (sentence level) and prime-target expressions (word level). Stimuli were presented acoustically and no overt behavioral response of the participants was required. Event-related brain potentials to target words preceded by true and false negated expressions were analyzed both within group and at the single subject level. Across the different processing conditions (word pairs and sentences), target words elicited a frontal negativity and a late positivity in the time window from 600–1000 msec post target word onset. Amplitudes of both brain potentials varied as a function of the truth value of the negated expressions. Results were confirmed at the single-subject level. In sum, our results support recent suggestions according to which evaluation of the truth value of a negated expression is a time- and cognitively demanding process that cannot be solved automatically, and thus requires conscious processing. Our paradigm provides insight into higher-order processing related to language comprehension and reasoning in healthy subjects. Future studies are needed to evaluate if our paradigm also proves sensitive for the detection of consciousness in non-responsive patients.

Learning-related shifts in generalization gradients for complex sounds

Learning to discriminate stimuli can alter how one distinguishes related stimuli. For instance, training an individual to differentiate between two stimuli along a single dimension can alter how that individual generalizes learned responses. In this study, we examined the persistence of shifts in generalization gradients after training with sounds. University students were trained to differentiate two sounds that varied along a complex acoustic dimension. The students were subsequently tested on their ability to recognize a sound that they had experienced during training when it was presented among several novel sounds varying along this same dimension. Peak shift was observed in Experiment 1, in which generalization tests immediately followed training, and in Experiment 2, in which the tests were delayed by 24 h. These findings further support the universality of generalization processes across species, modalities, and levels of stimulus complexity. They also raise new questions about the mechanisms underlying learning-related shifts in generalization gradients. The sound stimuli from this study are available as .wav files from http://lb.psychonomic-journals.org/content/supplemental.

Development of static and dynamic perception for luminance-defined and texture-defined information

The development of static and dynamic perception for stimuli requiring different levels of neural analysis was assessed by measuring orientation-identification and direction-identification thresholds for both lower-level [or first-order (FO)] and higher-level [or second-order (SO)] stimuli as a function of age. Results demonstrate that both lower-level and higher-level perception continue to develop during school-age years in both dynamic and static domains. When compared with adult levels, dynamic performance for 5-6-year-olds is significantly decreased for SO, but not for the FO perception; however, type of stimulus (FO vs. SO) did not affect the development of static perception. We therefore suggest that levels of stimulus complexity should be considered an important variable when assessing and making inferences regarding the typical and atypical development of static and dynamic perception.

Age-related deficits in generation and manipulation of mental images: I. The role of sensorimotor speed and working memory.

The authors investigated age-related slowing of information processing in mental imagery tasks. Eighty-five healthy adults (ages 18 to 77) performed a visual, sensorimotor, reaction-time task; a visual-perceptual choice reaction task; and 3 mental imagery tasks that varied in apparent difficulty and involved stimuli at 2 levels of graphic complexity. Age was associated with prolongation of response time across all tasks and both levels of stimulus complexity. Accuracy of response was adversely affected by increase in stimulus complexity in all tasks, whereas it was negatively related to age only on the tasks with substantial mental imagery requirements. Slowing of information processing and reduction in accuracy were mediated by declines in working memory but not by decrease of sensorimotor speed.

A Simultaneous Regression Model for Double Stimulation Tasks

Reaction time in double stimulation tasks was investigated, and a simultaneous regression model was proposed within the concept of variable capacity allocation theory. The model was tested using a double stimulation task paradigm. In the experiment, six levels of inter-stimulus interval (ISI) and three levels of stimulus complexity were employed. The regression analysis showed that the effects of stimulus complexity and ISI were significant. From the simultaneous regression model, reaction times to the first and to the second stimulus were predicted for the different experimental conditions.

A new processing model for predicting performance on Pascual-Leone's test of M-space

A new model is proposed for explaining children's performance on Pascual-Leone's test of M-space. The model differs from Pascual-Leone's in three regards. (1) It assumes that children do not stop sampling a compound stimulus until every simple stimulus in their field of attention has already been noticed and responded to. (2) It assumes that the probability of sampling different combinations of simple stimuli conforms to the laws of Maxwell-Boltzman statistics rather than Bose-Einstein statistics. (3) It assumes that children's ability to detect all the simple stimuli in a compound stimulus is highly dependent both on the relative saliencies of the simple stimuli and on the length of time for which the compound stimulus is exposed. Using the developmental values of M hypothesized by Pascual-Leone, and standard techniques of computer simulation, the new model is used to generate theoretical performance curves for children at four different age levels and seven different levels of stimulus complexity. It is shown that the predicted performance curves for an exposure time of 5 sec provide a reasonable fit to the data originally reported by Pascual-Leone (1970), and that the predicted performance curves for an exposure time of 10 sec provide a reasonable fit to data obtained more recently by Parkinson (1976). Finally, it is shown that the order of children's responses as well as the number of their responses can be predicted. Two conclusions are drawn. (1) The new processing model offers a viable alternative to the model originally proposed by Pascual-Leone. (2) Regardless of which processing model is employed, the M-values originally postulated by Pascual-Leone are valid.

Effects of moderate levels of blood alcohol on responses to information from simulated automobile rear-signal systems

The experiment investigated the effects of functional separation of brake and turn-signals, and of low levels of alcohol intoxication on a driver's ability to detect and interpret rear-signal information presented on a model automobile in a laboratory setting. Twelve experienced drivers performed the laboratory task for one-hour sessions on five successive days. Three independent variables were examined in a randomized-block factorial design. These consisted of two types of rear-signal systems, one with brake and turn-signals combined under the same lens, the other with brake and turn-signals under separate lenses, four levels of blood alcohol, and six levels of stimulus complexity. Response errors and the latencies between the onset of the stimulus and both the onset of the response and the completion of the response were measured. Results indicated that response variables were not equally sensitive to the task and that performance was significantly affected by model type and stimulus complexity. Performance deteriorated with blood alcohol levels as low as 0.05% on the combined model and 0.08% on the model that separated brake and turn-signal lights. Results are discussed in terms of the stimulus-identification/response-choice components of the task, and in terms of the optimum coding methods for rear signals.

Effects of Functional Separation and Low Levels of Blood Alcohol on the Response to Automobile Rear-Signal Information

The experiment investigated the effects of functional separation of brake and turn-signals, and of low levels of alcohol intoxication on a driver's ability to detect and interpret rear-signal information presented on a model automobile in a laboratory setting. Twelve experienced drivers performed the laboratory task for one-hour sessions on five successive days. Three independent variables were examined in a randomized-block, factorial design. These consisted of two levels of model type, one with brake and turn-signals combined under the same lens, the other with brake and turn-signals under separate lenses, four levels of blood alcohol, .00, .02, .05, and .08%, and six levels of stimulus complexity, representing six types of rear-signal information. Response variables consisted of response errors and the latencies between the onset of the stimulus and both the onset of the response and the completion of the response. Results indicated that the response variables were not equally sensitive to the task and that performance was significantly affected by model type and stimulus complexity. Performance deteriorated with blood alcohol levels as low as .05% on the combined model and 0.8% on the model that separated brake and turn-signal lights. Results are discussed in terms of the stimulus-identification/response-choice components of the task, and in terms of optimal coding methods for rear signals.

Infants' response to facelike patterns: Developmental changes between 10 and 15 weeks of age

Infants at two age levels were shown six patterns which represented three levels of stimulus complexity and two types of organization, facial and nonfacial. Ten-week-old infants showed a preference for the higher levels of complexity but acted as though they were oblivious to the type of organization which was imposed on the elements within the stimulus patterns. Fifteen week olds also showed increased attention to the higher levels of complexity. In addition, at the older age level differential responding was greater for stimuli which varied concomitantly in both facial resemblance and complexity (Facial organization) than for those which varied only in complexity (Nonfacial organization). The present results agree with those of previous studies in suggesting that there is a change between the ages of 10 and 15 weeks in the dimensions which underlie infants' response to facelike patterns.

Effects of two levels of stimulus complexity upon hypothesis sampling systems among second and sixth grade children

Groups of second and sixth grade children each solved a series of discrimination-learning problems involving four and eight dimensions that contained blanktrial probes for the S′s hypothesis ( H). There were significant effects of grade level on three dependent measures (learning, generating consistent H patterns, sampling locally consistent Hs). Main effects of stimulus complexity were significant on five measures (the three above, rejecting disconfirmed Hs, maintaining confirmed Hs). There were no interactions involving any of these measures. The hypothesis sampling system ( Sy) observed in each problem was also determined. Among sixth grade Ss this measure was unaffected by stimulus complexity level. Second grade Ss generated logically structured Sys in 65% of four-dimensional, but only 30% of eight-dimensional problems. They generated stereotyped behaviors or unsystematic sequences of Hs in 70% of eight-dimensional, but only about 35% of four-dimensional problems. Detailed analyses revealed that among second grade Ss good information processors (in terms of four component processes above) usually imposed a logical structure on four-dimensional, but generated unsystematic sequences of Hs in many of eight-dimensional problems. Poor processors generated stereotyped behaviors in both four- and eight-dimensional problems.

Varying degrees of complexity and isolation in visual exploration.

In two experiments viewing times were measured while Ss looked at random geometric forms. Stimuli were constructed to represent increasing levels of complexity. In both experiments, the relationship between level of stimulus complexity and viewing time was monotonic and increasing. The results are interpreted as supporting a meaning-processing model of visual exploration rather than theories concerning optimal levels of stimulation.

The effect of stimulus complexity on retrieval of information frown memory

Eighteen Ss performed an item recognition task involving memorized lists of one, two, and three nonsense forms at one of two levels of stimulus complexity. Analysis of RT-set size functions and serial position functions suggested that (a) when the memorized list consisted of simple figures, Ss engaged in a serial exhaustive search of items stored in memory prior to responding and (b) when the memorized items were complex, an increase in set size was accompanied by a change in search strategy from a backward self-terminating search to a random self-terminating search.

Task complexity and serial performance under steadily increasing input rates.

Twenty-seven subjects were trained on a multichannel information processing task, under three levels of stimulus complexity, and tested in these conditions in each of three 5-min. sessions of rapidly increasing input rate. Correct responses, errors, and omissions were examined for each condition. During testing, performance decrements which followed initial performance peaks occurred at lower input rates were least severe, and recovery was quickest when stimulus complexity was greatest. Subjects adapted to high input rates by filtering and making omissions rather than incorrect responses. In addition two types of attention strategies were identified, one of which produced superior performance at low input rates, and the other superior performance at high input rates. Error and response rates were positively correlated for all code complexity levels when pooled across subjects. However, at the most complex level this relation only held for one of the two attention strategies when the two sets of data were analyzed separately.