Increasing Stimulus Complexity Research Articles

Eye‐tracking for longitudinal assessment of social cognition in children born preterm

Preterm birth is associated with atypical social cognition in infancy, and cognitive impairment and social difficulties in childhood. Little is known about the stability of social cognition through childhood, and its relationship with neurodevelopment. We used eye-tracking in preterm and term-born infants to investigate social attentional preference in infancy and at 5years, its relationship with neurodevelopment and the influence of socioeconomic deprivation. A cohort of 81 preterm and 66 term infants with mean (range) gestational age at birth 28+5 (23+2 -33+0 ) and 40+0 (37+0 -42+1 ) respectively, completed eye-tracking at 7-9months, with a subset re-assessed at 5years. Three free-viewing social tasks of increasing stimulus complexity were presented, and a social preference score was derived from looking time to socially informative areas. Socioeconomic data and the Mullen Scales of Early Learning at 5years were collected. Preterm children had lower social preference scores at 7-9months compared with term-born controls. Term-born children's scores were stable between time points, whereas preterm children showed a significant increase, reaching equivalent scores by 5years. Low gestational age and socioeconomic deprivation were associated with reduced social preference scores at 7-9months. At 5years, preterm infants had lower Early Learning Composite scores than controls, but this was not associated with social attentional preference in infancy or at 5years. Preterm children have reduced social attentional preference at 7-9months compared with term-born controls, but catch up by 5years. Infant social cognition is influenced by socioeconomic deprivation and gestational age. Social cognition and neurodevelopment have different trajectories following preterm birth.

Stimulus complexity and chunk tightness interact to impede perceptual restructuring during problem solving

The mutual influence of stimulus complexity and chunk tightness on perceptual restructuring was examined using a chunk decomposition task (CDT). Participants attempted to remove components of Chinese characters in order to produce new, valid characters. Participants had their electroencephalogram recorded while completing a CDT in conditions of low or high stimulus complexity, crossed with two levels of chunk tightness. Tight chunks overlapped spatially whereas loose chunks did not. Both increasing chunk tightness and increasing stimulus complexity impaired performance (lower accuracy, longer reaction times), and these factors interacted such that highly complex, tight chunks produced the worst performance. These factors also had interacting effects on the late positive complex (LPC). The LPC amplitude was reduced by increasing chunk tightness, but this effect was attenuated for highly complex stimuli. These results suggest that though chunk tightness and stimulus complexity impair performance in the CDT, they have dissociable neural underpinnings.

Emotion-in-Motion, a Novel Approach for the Modification of Attentional Bias: An Experimental Proof-of-Concept Study.

BackgroundIndividuals with heightened anxiety vulnerability tend to preferentially attend to emotionally negative information, with evidence suggesting that this attentional bias makes a causal contribution to anxiety vulnerability. Recent years have seen an increase in the use of attentional bias modification (ABM) procedures to modify patterns of attentional bias; however, often this change in bias is not successfully achieved.ObjectiveThis study presents a novel ABM procedure, Emotion-in-Motion, requiring individuals to engage in patterns of attentional scanning and tracking within a gamified, complex, and dynamic environment. We aimed to examine the capacity of this novel procedure, as compared with the traditional probe-based ABM procedure, to produce a change in attentional bias and result in a change in anxiety vulnerability.MethodsWe administered either an attend-positive or attend-negative version of our novel ABM task or the conventional probe-based ABM task to undergraduate students (N=110). Subsequently, participants underwent an anagram stressor task, with state anxiety assessed before and following this stressor.ResultsAlthough the conventional ABM task failed to induce differential patterns of attentional bias or affect anxiety vulnerability, the Emotion-in-Motion training did induce a greater attentional bias to negative faces in the attend-negative training condition than in the attend-positive training condition (P=.003, Cohen d=0.87) and led to a greater increase in stressor-induced state anxiety faces in the attend-negative training condition than in the attend-positive training condition (P=.03, Cohen d=0.60).ConclusionsOur novel, gamified Emotion-in-Motion ABM task appears more effective in modifying patterns of attentional bias and anxiety vulnerability. Candidate mechanisms contributing to these findings are discussed, including the increased stimulus complexity, dynamic nature of the stimulus presentation, and enriched performance feedback.

Stimulus space complexity determines the ratio of specialist and generalist neurons during pattern recognition

Neural processing layers built on divergent connectivity patterns display two types of stimulus-dependent responses: neurons that react to a few stimuli, specialists, and other ones that respond to a wide range of inputs, generalists. Specialists are essential for the discrimination of stimuli and generalists extract common and generic properties from them. This neural heterogeneity could have emerged because of animal adaptation to the environment. Thus, we suggest that there is a relationship between the percentage of specialists and generalists and the stimulus complexity. In order to study this possible relationship, we use patterns with different complexities in a bio-inspired neural network and calculate their classification errors for different ratios of these types of neurons. This study shows that, when the complexity of the stimuli is low, the minimum classification error is achieved with almost any specialist-generalist ratio. Thus, in this case, the role of these neurons during pattern recognition is unspecific. When this complexity is intermediate, both are needed to minimize the classification error, usually in a similar proportion. For increasing stimulus complexity, the importance of generalists decreases, until their relevance is fully nullified when the complexity is high. Therefore, if we adjust the specialist-generalist ratio to the complexity of patterns, we can build more effective neural networks for pattern recognition. Finally, we propose an estimation of stimulus complexity based on the proportion of these types of neurons observed by neural recordings. This offers the possibility to evaluate the stimulus complexity to which animals are adapted.

In Search of Baseline: Absolute and Relative Measures of Blood Flow and Oxidative Metabolism in Visual Cortex Stimulated at Three Levels of Complexity

Objective: Functional imaging of regional cerebral blood flow (rCBF) or the blood-oxygenation-level dependent (BOLD) signal is based on the premise that changes of flow and energy metabolism are linked to the same incremental excitation of neurons. The baseline conjecture holds that a single default mode of brain function gives rise to coupled changes of blood flow and oxidative metabolism that raise oxygen’s extraction fraction, when activity falls, and lower the extraction fraction when activity rises. To locate the hypothetical baseline in visual cortex in relation to functional demands, we compared increments of (rCBF) and oxidative metabolism (rCMRO2) during stimulation of visual cortex at three different levels of complexity. Materials and Methods: Healthy volunteers underwent positron emission tomography (PET) with [15O] water and [15O] oxygen while they viewed three stimuli in random order; a cross-hair fixation stimulus without color or spatial frequency (FX), an achromatic white disc stimulus with an 8 Hz on-off rate (WD), and a circular yellow-blue chromatic checkerboard with an 8 Hz color-reversing frequency (YB). For the baseline conjecture to hold, the sum of any pair of contrasts must equal the third at any site of significant change, such that the sum of the contrasts [YB-WD] and [WD-FX] must equal the contrast [YB-FX]. Results: The rCMRO2 and rCBF changes averaged 21% and 52% of the whole-brain average, implying excitation by increasing stimulus complexity. The color reversal contrast ([YB-WD]) revealed bilateral sites of significant change of rCMRO2 and a single left hemisphere site of significant rCBF change in the general region of Brodmann’s areas (BA) 17 and 18 of the lingual gyrus. The spatial frequency contrasts ([YB-FX] and [WD-FX]) revealed single sites of significant change of rCMRO2 and rCBF also in the lingual gyrus but close to the midline. For the midline sites, the [YB-FX] and [WD-FX] contrasts were identical and revealed a baseline between the FX and WD/YB stimulus conditions. For the lateral sites, the [YB-WD] stimulus contrast revealed a baseline between the YB and WD stimulus conditions. Conclusion: The intermediate positions of the baselines indicated the existence in BA 17/18 of at least two populations of cells, a lateral group responding to the absence and presence of color reversal in the presence of a spatial frequency, and a midline group responding only to the absence and presence of spatial frequency.

Music-based rehabilitation in cochlear implant users: Insights from brain-plasticity research

Music-based rehabilitation in cochlear implant users: Insights from brain-plasticity research

Previous exposure to intact speech increases intelligibility of its digitally degraded counterpart as a function of stimulus complexity

Recent studies have shown that acoustically distorted sentences can be perceived as either unintelligible or intelligible depending on whether one has previously been exposed to the undistorted, intelligible versions of the sentences. This allows studying processes specifically related to speech intelligibility since any change between the responses to the distorted stimuli before and after the presentation of their undistorted counterparts cannot be attributed to acoustic variability but, rather, to the successful mapping of sensory information onto memory representations. To estimate how the complexity of the message is reflected in speech comprehension, we applied this rapid change in perception to behavioral and magnetoencephalography (MEG) experiments using vowels, words and sentences. In the experiments, stimuli were initially presented to the subject in a distorted form, after which undistorted versions of the stimuli were presented. Finally, the original distorted stimuli were presented once more. The resulting increase in intelligibility observed for the second presentation of the distorted stimuli depended on the complexity of the stimulus: vowels remained unintelligible (behaviorally measured intelligibility 27%) whereas the intelligibility of the words increased from 19% to 45% and that of the sentences from 31% to 65%. This increase in the intelligibility of the degraded stimuli was reflected as an enhancement of activity in the auditory cortex and surrounding areas at early latencies of 130–160ms. In the same regions, increasing stimulus complexity attenuated mean currents at latencies of 130–160ms whereas at latencies of 200–270ms the mean currents increased. These modulations in cortical activity may reflect feedback from top-down mechanisms enhancing the extraction of information from speech. The behavioral results suggest that memory-driven expectancies can have a significant effect on speech comprehension, especially in acoustically adverse conditions where the bottom-up information is decreased.

Multisensory temporal integration in autism spectrum disorders.

The new DSM-5 diagnostic criteria for autism spectrum disorders (ASDs) include sensory disturbances in addition to the well-established language, communication, and social deficits. One sensory disturbance seen in ASD is an impaired ability to integrate multisensory information into a unified percept. This may arise from an underlying impairment in which individuals with ASD have difficulty perceiving the temporal relationship between cross-modal inputs, an important cue for multisensory integration. Such impairments in multisensory processing may cascade into higher-level deficits, impairing day-to-day functioning on tasks, such as speech perception. To investigate multisensory temporal processing deficits in ASD and their links to speech processing, the current study mapped performance on a number of multisensory temporal tasks (with both simple and complex stimuli) onto the ability of individuals with ASD to perceptually bind audiovisual speech signals. High-functioning children with ASD were compared with a group of typically developing children. Performance on the multisensory temporal tasks varied with stimulus complexity for both groups; less precise temporal processing was observed with increasing stimulus complexity. Notably, individuals with ASD showed a speech-specific deficit in multisensory temporal processing. Most importantly, the strength of perceptual binding of audiovisual speech observed in individuals with ASD was strongly related to their low-level multisensory temporal processing abilities. Collectively, the results represent the first to illustrate links between multisensory temporal function and speech processing in ASD, strongly suggesting that deficits in low-level sensory processing may cascade into higher-order domains, such as language and communication.

Inducing closing-in phenomenon in healthy young adults: the effect of dual task and stimulus complexity on drawing performance

Closing-in (CI) is the tendency to act very close to the model in tasks such as drawing, 3D construction, gesture imitation, or writing. Closing-in is observed in degenerative and focal brain diseases, but also in normally developing children. In the present paper, three experiments were conducted to evaluate whether CI can be triggered during a copying task in normal young adults by increasing stimulus complexity and attentional load. Participants were required to copy complex lines in one of three conditions: without interfering activities (baseline), during counting, or during execution of a 2-back short-term memory task. In Experiment 1, participants were required to reproduce horizontally aligned stimuli, starting from a dot placed below each stimulus and proceeding from left to right; in Experiment 2, stimuli were again horizontally aligned, but the starting dot was placed above each stimulus, and writing proceeded from right to left; in Experiment 3, stimuli were aligned vertically and copying proceeded in upward direction. Results from all experiments showed that when normal young adults are engaged in an attentional-demanding concurrent activity, they tend to approach to the model, whereas the effect of stimulus complexity disappeared with unusual writing direction (Experiments 2 and 3). These findings demonstrate that even in normal young adults, a reduction in available attentional resources can release an attraction toward the model.

FMRI task parameters influence hemodynamic activity in regions implicated in mental set switching.

Mental set switching is a complex executive function that is required when the focus of attention must be altered in order to adapt to a frequently-changing environment. While there is generally acceptance that switching is subserved by a fronto-parietal network, there is a considerable lack of consistency across studies as to other brain regions involved in executing mental set switches. This functional magnetic resonance imaging study sought to determine whether paradigmatic design aspects such as stimulus complexity, motor response complexity, and stimulus ordering could account for the differences in reporting of brain regions associated with mental set switching across previous studies. Several brain regions, including the striatum and anterior cingulate, previously associated with mental set switching were found to be related more to resolving intra-stimulus interference conferred by increased stimulus complexity and increased motor response complexity than to executing the mental set switch. In considering stimulus ordering, defined as the number of non-switch trials preceding a switch trial, brain activity was not observed in the fronto-parietal regions typically associated with switching but rather in regions in the anterior prefrontal cortex, sensorimotor cortex, and secondary visual cortices. Our results indicate that these important paradigm design aspects that are theoretically unrelated to set switching per se should be balanced and controlled for in future experiments, so as not to obscure clear identification of brain regions truly engaged in mental set switching.

Variations in recollection: The effects of complexity on source recognition.

Whether recollection is a threshold or signal detection process is highly controversial, and the controversy has centered in part on the shape of receiver operating characteristics (ROCs) and z-transformed ROCs (zROCs). U-shaped zROCs observed in tests thought to rely heavily on recollection, such as source memory tests, have provided evidence in favor of the threshold assumption, but zROCs are not always as U-shaped as threshold theory predicts. Source zROCs have been shown to become more linear when the contribution of familiarity to source discriminations is increased, and this may account for the existing results. However, another way in which source zROCs may become more linear is if the recollection threshold begins to break down and recollection becomes more graded and Gaussian. We tested the "graded recollection" account in the current study. We found that increasing stimulus complexity (i.e., changing from single words to sentences) or increasing source complexity (i.e., changing the sources from audio to videos of speakers) resulted in flatter source zROCs. In addition, conditions expected to reduce recollection (i.e., divided attention and amnesia) had comparable effects on source memory in simple and complex conditions, suggesting that differences between simple and complex conditions were due to differences in the nature of recollection, rather than differences in the utility of familiarity. The results suggest that under conditions of high complexity, recollection can appear more graded, and it can produce curved ROCs. The results have implications for measurement models and for current theories of recognition memory.

157. Gender differences in event-related potentials elicited by visual stimuli of increasing stimulus complexity

157. Gender differences in event-related potentials elicited by visual stimuli of increasing stimulus complexity

Dynamic encoding of pitch, timing, and timbre.

The perception of music depends on three fundamental elements: pitch, timing, and timbre. It is possible to access the neural transcription of these elements objectively, noninvasively, and with great fidelity with scalp electrodes in humans. The effects of musical experience on subcortical encoding of sound are pervasive and extend beyond music to the domains of language and emotion. The acoustic cues relating to pitch, timing, and timbre have distinct representations, which can be selectively enhanced or degraded in different populations. Musically trained subjects have enhanced subcortical representation of pitch, timing, and timbre, although with increased stimulus complexity, timbre cues become more pronounced while pitch cues are diminished. Musical experience fundamentally shapes auditory processing that occurs early in the sensory processing stream. This top‐down influence is likely mediated by the extensive (corticofugal) circuitry of descending efferent fibers that synapse all along the auditory pathway. Sensory shaping occurs not only with lifelong experience but can be effected by short‐term training. I will discuss a series of experiments demonstrating the lifelong and short‐term malleability of the neural encoding of pitch, timing, and timbre in the auditory brainstem. [Work supported by National Institutes of Health (R01DC001510) and National Science Foundation (NSF 0544846).

Gender differences in event-related potentials elicited by visual stimuli of increasing stimulus complexity

Gender differences in event-related potentials elicited by visual stimuli of increasing stimulus complexity

The Effects of Increasing Stimulus Complexity in Event-Related Potentials and Reaction Time Testing: Clinical Applications in Evaluating Patients with Traumatic Brain Injury

This study compared the effectiveness of P300 event related potentials (ERPs) and reaction time (RT) in discriminating patients with traumatic brain injury (TBI) from healthy control subjects. In particular, we examined how the use of more complex, ecologically relevant stimuli may affect the clinical utility of these tasks. We also evaluated how length of posttraumatic amnesia (PTA) and loss of consciousness (LOC) related to P300 and RT measures in our patient sample. There were 22 subjects (11 patients with TBI and 11 age-matched healthy control subjects). Four stimulus detection procedures were used: two using simple, conventional stimuli (auditory tone discrimination, AT; visual color discrimination, VC), and two using complex, ecologically relevant stimuli in the auditory and visual modalities (auditory word category discrimination, AWC; visual facial affect discrimination, VFA). Our results showed that RT measures were more effective in identifying TBI patients when complex stimuli were used (AWC and VFA). On the other hand, ERP measures were more effective in identifying TBI patients when simple stimuli were used (AT and VC). We also found a remarkably high correlation between duration of PTA and P300 amplitude.

Enrichment-dependent differences in novelty exploration in rats can be explained by habituation

In rats, exploratory activity and emotional reactivity towards novel stimuli reflect independent biological functions that are modulated differently by rearing experiences. Environmental enrichment is known to improve performance in exploratory tasks, while having inconsistent effects on emotionality. This study examined the effect of environmental enrichment on the behaviour of rats in two exploratory tasks. Male rats were reared under one of four conditions, differing in social and non-social complexity. At 9 weeks of age, exploration of a novel open field, and exploration of novel objects in the same open field following 24 h habituation, was assessed. Differences in social and non-social complexity of the rearing environment had inconsistent effects on exploration in the novel open field. In contrast, when rats were faced with novel objects in an otherwise familiar environment, exploration habituated faster with increasing stimulus complexity of the non-social environment. The social environment had no effect on this latter test. These findings indicate that environmental enrichment affects exploratory activity primarily through its effect on habituation to novelty. This effect depends on relative stimulus complexity of the rearing environment, but is independent of social factors. The present results further suggest that aversive tasks can obscure the expression of enrichment-dependent differences in habituation to novelty.

Learning generalisation and localisation: Competition for stimulus type and receptive field

The evidence from neurophysiological recordings from the primate visual system suggests that sensory patterns are processed using units arranged in a hierarchical multi-layered network. Responses of these units show progressively increasing receptive field size combined with selectivity for increasing stimulus complexity at successively higher levels. It is argued that the rate of the increase in receptive field size is less than the maximum possible given the initial spread of neuronal projections that occurs during development. We show here that a competitive learning mechanism using a ‘trace-Hebbian’ learning rule [14] with a larger number of competing output units learns not only positional invariance for a given input feature but can also establish restricted receptive field sizes (i.e. less than the maximum size given the initial connections). Importantly the same stimulus selectivity was maintained throughout the receptive field. It is shown that this is accompanied by a relative increase in the spatial evenness of the representation of each detector type across position within the input array. The network properties were found to be robust and stable over a wide range of learning parameters. We suggest that such a competitive mechanism may help account for the reported properties of cells in the ventral stream of the primate visual system.

Sweetness suppression in fructose/citric acid mixtures: a study of contextual effects.

Two experiments investigated whether stimulus context affects ratings for mixtures of dissimilartasting substances (fructose/citric acid) to the same degree that it affects ratings for unmixed substances (fructose). In Experiment 1, replacing mixtures by equisweet unmixed fructose solutions produced virtually no response shifts. The proportion of mixtures in the stimulus set affected only slightly the degree of mixture suppression inferred from the responses. In Experiment 2, both the stimulus type (mixed or unmixed) and the stimulus distribution (positively versus negatively skewed) affected the responses. Several factors that determine the impact of contextual changes are identified: (a) the stage in stimulus processing affected--that of representation on the internal continuum or that of response selection; (b) the size and sources of variation in the affected process; and (c) the degree to which a stimulus is perceptually integrated in the context. In the present study, the sweetness of fructose/citric acid mixtures was largely, but not completely, integrated with the sweetness of unmixed fructose solutions. It is suggested that increased stimulus complexity makes mixture ratings more susceptible to contextual shifts. An analysis relating the size of the contextual shift to the degree of response variability suggests that response-selection processes are more important in determining the responses for unmixed stimuli than they are in determining the responses for mixtures.

Developmental changes in the duration of attention to unfamiliar stimuli in the rat.

The purpose of the present study was to examine developmental changes in the duration of attention to novel auditory stimuli in rats from infancy to adulthood. In all experiments, the cardiac component of the orienting response was used as the index of attention. In the first experiment 16-, 23-, 30-, and 75-day-old rats were exposed to a novel auditory stimulus for 60 s. Animals of all four ages exhibited a marked decrease in heart rate in response to this stimulus. Although there were no significant effects of age on the magnitude of the cardiac response, there were dramatic developmental differences in the persistence of the response. The 16-day-olds maintained a decrease in heart rate for the entire stimulus period, whereas heart rate returned to baseline in the 75-day-olds after only 40 s. The duration of the cardiac response of the 23- and 30-day-olds was between these extremes. In Experiments 2A and 2B the effect of stimulus complexity on duration of the cardiac response was examined. Increasing stimulus complexity prolonged the deceleratory response in the 30-day-olds (Experiment 2A), and decreasing stimulus complexity decreased the duration of the cardiac response in the 16-day-olds (Experiment 2B). The results of these experiments were discussed in the context of Cohen's and Porges's two-phase theories of attention. The findings demonstrate that the initial attention-getting or reactive phase of attention did not change with age, but that the duration of the attention-holding or sustained phase decreased substantially during development.

Human response to cyclofusional stimuli containing depth cues.

The cyclofusional response to stimuli containing depth cues was studied. Eye positions were monitored by an objective, binocular, eye movement measuring technique while a psychophysical method was used to measure the stereoscopic responses. We found that the overall response contains both stereoscopic and cyclofusional components and that the cyclofusional response includes a large nonmotor, or sensory, contribution. The composition of the response was unaffected by changes in stimulus size. Increased stimulus complexity elicited larger cyclotorsional eye movements and diminished the amount of perceived inclination which was observed in the fused percept.