Sample Stimuli Research Articles

Teaching identity matching of braille characters to beginning braille readers.

We taught three children with visual impairments to make tactile discriminations of the braille alphabet within a matching-to-sample format. That is, we presented participants with a braille character as a sample stimulus, and they selected the matching stimulus from a three-comparison array. In order to minimize participant errors, we initially arranged braille characters into training sets in which there was a maximum difference in the number of dots comprising the target and nontarget comparison stimuli. As participants mastered these discriminations, we increased the similarity between target and nontarget comparisons (i.e., an approximation of stimulus fading). All three participants' accuracy systematically increased following the introduction of this identity-matching procedure.

The Effects of an Auditory Matching iPad App on Three Preschoolers' Echoic and Listener Responses.

We investigated the effects of an auditory match-to-sample protocol on three preschoolers' accurate echoics to 100 English words and advanced listener responses. The protocol was presented by using an iPad app Sounds the same: an app to target listening and speaking clearly. We used a combination of a multiple probe design (for echoic responses) and a delayed multiple probe design (for advanced listener literacy responses) with a time-lagged baseline across participants to test the effectiveness of the protocol. The three participants ranged from 4 to 5years old and were all diagnosed as preschoolers with disabilities. They were taught to discriminate between positive and negative exemplars of progressively more difficult sounds, words, and phases by matching the sample stimulus to the matching exemplar. Our data show that the mastery of the intervention resulted in increases in the accuracy of the participants' articulation of their echoics, as well as their advanced listener repertoires as measured by the responses to spoken directions in the presence of visual distractors.

Pre-encoding gamma-band activity during auditory working memory

Previous magnetoencephalography (MEG) studies have revealed gamma-band activity at sensors over parietal and fronto-temporal cortex during the delay phase of auditory spatial and non-spatial match-to-sample tasks, respectively. While this activity was interpreted as reflecting the memory maintenance of sound features, we noted that task-related activation differences might have been present already prior to the onset of the sample stimulus. The present study focused on the interval between a visual cue indicating which sound feature was to be memorized (lateralization or pitch) and sample sound presentation to test for task-related activation differences preceding stimulus encoding. MEG spectral activity was analyzed with cluster randomization tests (N = 15). Whereas there were no differences in frequencies below 40 Hz, gamma-band spectral amplitude (about 50–65 and 90–100 Hz) was higher for the lateralization than the pitch task. This activity was localized at right posterior and central sensors and present for several hundred ms after task cue offset. Activity at 50–65 Hz was also increased throughout the delay phase for the lateralization compared with the pitch task. Apparently cortical networks related to auditory spatial processing were activated after participants had been informed about the task.

Relation between Exclusion and Stimulus Equivalence Class Formation in Auditory-Visual and Visual-Visual Matching in Preschoolers

The hypothesis that exclusion performance is a prerequisite for the stimulus equivalence class formation was assessed in preschoolers of about 5 years of age. In Experiment 1, two groups of children were trained in a set of conditional discriminations in a two-choice matching to sample format, Group 1 in an auditory-visual modality baseline, and Group 2 in a visual-visual modality baseline. Exclusion test trials included an undefined (not previously related) comparison stimulus, and a defined (i.e., related in the baseline) comparison stimulus, in the presence of an undefined sample stimulus. Selection of the undefined comparison was recorded as a correct response. Stimulus equivalence class formation was assessed by way of symmetry and transitivity test trials. Experiment 2 replicated the design of the first experiment, with the difference that exclusion was assessed independently and with a different baseline from symmetry and transitivity. Exclusion scores were higher for the auditory-visual groups than the visual-visual groups. In both modalities symmetry scores were superior to those in transitivity. Symmetry showed independent from the exclusion performance, but transitivity was presumably dependent from it in the auditory-visual modality.

Effects of stimulus meaningfulness on the acquisition of conditional relations and the emergence of symmetrical relations in adult humans

ABSTRACTThe goal of the present study was to investigate the effects of stimulus meaningfulness of sample and comparison stimuli on the acquisition of conditional relations and the emergence of symmetrical relations. Eight college students were trained on two types of baseline conditional discrimination tasks involving meaningful (English words) and non-meaningful (Swahili words) stimuli. One task involved English samples and Swahili comparisons (English–Swahili), whereas the other task involved Swahili samples and English comparisons (Swahili–English). Test trials, without programmed consequences, presented the symmetry probe of the baseline relations trained. That is, the English–Swahili baseline relations presented on the training trials were presented as the Swahili–English symmetrical relations on the test trials. Similarly, the Swahili–English baseline relations on the training trials were presented as the English–Swahili symmetrical relations on the test trials. The results show that the English–Swahili baseline relations were acquired faster than the Swahili–English baseline relations. The results also show that, relative to the acquisition of the baseline relations, the emergence of symmetrical relations was facilitated and delayed, respectively, on the English–Swahili and Swahili–English test trials. The present results suggest that stimulus meaningfulness of untrained successive discrimination of samples and simultaneous discrimination of comparisons on test trials affects the emergence of symmetrical relations, with the former playing a more important role than the latter.

Reducing overselective stimulus control with differential observing responses.

Overselective stimulus control refers to discriminative control in which the number of controlling stimuli is too limited for effective behavior. Experiment 1 included 22 special-education students who exhibited overselective stimulus control on a two-sample delayed matching task. An intervention added a compound identity matching opportunity within the sample observation period of the matching trials. The compound matching functioned as a differential observing response (DOR) in that high accuracy verified observation and discrimination of both sample stimuli. Nineteen participants learned to perform the DOR and two-sample delayed matching accuracy increased substantially for 16 of them. When the DOR was completely withdrawn after 10 sessions, accuracy declined. In Experiment 2, a more gradual withdrawal of DOR requirements showed that highly accurate performance could be maintained with the DOR on only a proportion of trials for most participants. The results show that DOR training may lead to a general improvement in observing behavior.

Encoding of global visual motion in the nidopallium caudolaterale of behaving crows.

Songbirds possess acute vision. How higher brain centres represent basic and parameterised visual stimuli to process sensory signals according to their behavioural importance has not been studied in a systematic way. We therefore examined how carrion crows (Corvus corone) and their nidopallial visual neurons process global visual motion information in dynamic random-dot displays during a delayed match-to-sample (DMS) task. The behavioural data show that moderately fast motion speeds (16° of visual angle/s) result in superior direction discrimination performance. To characterise how neurons encode and maintain task-relevant visual motion information, we recorded the single-unit activity in the telencephalic association area 'nidopallium caudolaterale' (NCL) of behaving crows. The NCL is considered to be the avian analogue of the mammalian prefrontal cortex. Almost a third (28%) of randomly selected NCL neurons responded selectively to the motion direction of the sample stimulus, mostly to downward motions. Only few NCL neurons (7.5%) responded consistently to specific motion directions during the delay period. In error trials, when the crows chose the wrong motion direction, the encoding of motion direction was significantly reduced. This indicates that sensory representations of NCL neurons are relevant to the birds' behaviour. These data suggest that the corvid NCL, even though operating at the apex of the telencephalic processing hierarchy, constitutes a telencephalic site for global motion integration.

Neural correlates of sample-coding and reward-coding in the delay activity of neurons in the entopallium and nidopallium caudolaterale of pigeons (Columba livia)

We recorded neuronal activity from the nidopallium caudolaterale, the avian equivalent of mammalian prefrontal cortex, and the entopallium, the avian equivalent of the mammalian visual cortex, in four birds trained on a differential outcomes delayed matching-to-sample procedure in which one sample stimulus was followed by reward and the other was not. Despite similar incidence of reward-specific and reward-unspecific delay cell types across the two areas, overall entopallium delay activity occurred following both rewarded and non-rewarded stimuli, whereas nidopallium caudolaterale delay activity tended to occur following the rewarded stimulus but not the non-rewarded stimulus. These findings are consistent with the view that delay activity in entopallium represents a code of the sample stimulus whereas delay activity in nidopallium caudolaterale represents a code of the possibility of an upcoming reward. However, based on the types of delay cells encountered, cells in NCL also code the sample stimulus and cells in ENTO are influenced by reward. We conclude that both areas support the retention of information, but that the activity in each area is differentially modulated by factors such as reward and attentional mechanisms.

Categorical Discrimination of Sequential Stimuli: All SΔ Are Not Created Equal

Pigeons were exposed to a novel variation of a stimulus discrimination task previously used with rats as a slot machine analog. We sought to replicate and extend characterizations of structural characteristics of responding, determine relations between those characteristics and identify predictors of individual differences in performance. Pecking during a “collect” phase produced food if and only if the keylight was red for the entire sample phase. In other trial types, the keylight was green, or started red and turned green after one or two pecks. The opportunity to respond was available for 5 s in all collect phases, permitting multiple responses per trial. Pigeons were less likely to peck in collect phases when sample stimuli were not all red, and when they did peck, it was at a lower rate. However, consistent with reactions to near wins in other slot machine tasks, there was more responding in collect phases that followed sample phases when the red keylight turned green after two pecks. Among initial response characteristics, response rate in trials that resembled near wins was the best predictor of terminal responding. Supporting their characterization as measures of stimulus control, collect proportions were negatively correlated with response times in the sample phase. Supporting their characterization as measures of conditioned reinforcing value, latency and response rate in collect phases were positively correlated, but neither was systematically correlated with proportion or sample phase response times. Ultimately, isolating measures of stimulus control and conditioned reinforcement may help determine the mechanisms responsible for near-win effects.

Visual priming and perception of small pictures in a scene with multiscale objects

Biederman and co-authors [1, 2], have shown that the priming effect in the long-tirn priming paradigm does not depend on the difference between the angular sizes of the test stimulus and the primer. However, these two and other similar works (both with long-time and short-fime priming paradigms) studied a small range of the angular sizes of stimuli. In Vakhrameeva et al. [3], it has been shown that there exist two perceptionally different size ranges: perception of the objects with angular size varying from 1-1.5 to 50 deg was found to be invariant, but for the objects which angular size is less than 1-1.5 deg (depending on object class and task) their perception is no longer invariant. In this work we have investigated the presence of priming effect in match-to-sample task with such a difference in the angular sizes of a primer and a test stimuli, when the sizes of the primer (about 4 deg) and the test stimulus (about 0.5 deg) belong to those different physiological size ranges. The sample stimulus was presented with and without the noise superposition. It has been shown that the priming effect is suppressed when the size difference between the primer and the test stimulus is large. A congruent primer can give a positive impact on the recognition of the test objects, but this takes place under viewing conditions complicated by the noise superposition.

Brief Report: A Preference for Biological Motion Predicts a Reduction in Symptom Severity 1 Year Later in Preschoolers with Autism Spectrum Disorders.

Recent research has consistently demonstrated reduced orienting to social stimuli in samples of young children with autism spectrum disorders (ASD). However, social orienting greatly varies between individual children on the spectrum. Better understanding this heterogeneity in social orienting may contribute to our comprehension of the mechanisms underlying autistic symptoms thereby improving our ability to intervene. Indeed, children on the autism spectrum who show higher levels of interest in social stimuli demonstrate reduced clinical symptoms and increased adaptive functioning. However, longitudinal studies examining the influence of social orienting on subsequent outcome are critically lacking. Here, we aim to explore the relationship between social interest at the age of 3 and changes in severity of autistic symptoms over the subsequent year, in 20 children with ASD and 20 age-matched typically developing (TD) children. A visual preference for social stimuli was measured using an eye-tracking task at baseline, consisting of a previously studied visual preference paradigm presenting biological and geometric motion side-by-side. The task was altered for the current study by alternating presentation side for each type of stimuli to keep visual perseveration from influencing participants’ first fixation location. Clinical data were collected both at baseline and 1 year later at follow-up. As a group, we observed reduced interest for biological motion (BIO-M) in children with ASD compared to TD children, corroborating previous findings. We also confirmed that a preference for BIO-M is associated with better adaptive functioning in preschoolers with ASD. Most importantly, our longitudinal results showed that a preference for BIO-M strongly predicted decreased severity of diagnostic symptoms. Participants who preferred social stimuli at the age of 3 showed drastic reductions in their severity level of autistic symptoms 1 year later, whereas participants who preferred geometric stimuli showed autistic symptoms that were unchanged or more severe after 1 year. As a whole, our results suggest that a preference for BIO-M may be key to understanding the behavioral phenotype of young children with ASD, and may represent a promising candidate behavior for predicting early developmental trajectories and outcome.

Multiple foci of spatial attention in multimodal working memory

The maintenance of sensory information in working memory (WM) is mediated by the attentional activation of stimulus representations that are stored in perceptual brain regions. Using event-related potentials (ERPs), we measured tactile and visual contralateral delay activity (tCDA/CDA components) in a bimodal WM task to concurrently track the attention-based maintenance of information stored in anatomically segregated (somatosensory and visual) brain areas. Participants received tactile and visual sample stimuli on both sides, and in different blocks, memorized these samples on the same side or on opposite sides. After a retention delay, memory was unpredictably tested for touch or vision. In the same side blocks, tCDA and CDA components simultaneously emerged over the same hemisphere, contralateral to the memorized tactile/visual sample set. In opposite side blocks, these two components emerged over different hemispheres, but had the same sizes and onset latencies as in the same side condition. Our results reveal distinct foci of tactile and visual spatial attention that were concurrently maintained on task-relevant stimulus representations in WM. The independence of spatially-specific biasing mechanisms for tactile and visual WM content suggests that multimodal information is stored in distributed perceptual brain areas that are activated through modality-specific processes that can operate simultaneously and largely independently of each other.

The role of the dorsolateral prefrontal cortex in early threat processing: a TMS study.

Previous studies demonstrated that excitatory (high frequency) offline transcranial magnetic stimulation (TMS) over the left and right dorsolateral prefrontal cortex (DLPFC) modulates attention allocation on threatening stimuli in non-clinical samples. These studies only employed offline TMS protocol that did not allow investigating the effect of the stimulation on the early stage of threat processing. In this study, the role of the right and left dorsolateral prefrontal cortex in early threat processing was investigated in high and low anxious individuals by means of an inhibitory single-pulse online TMS protocol. Our results demonstrated the role of the left DLPFC in an early stage of threat processing and that this effect is modulated by individuals' anxiety level. The inhibitory stimulation of the left DLPFC determined a disengagement bias in high anxious individuals, while the same stimulation determined an attentional avoidance in low anxious individuals. The findings of the present study suggest that right and left DLPFC are differently involved in early threat processing of healthy individuals.

Assessing generative braille responding following training in a matching-to-sample format.

We evaluated the effects of teaching sighted college students to select printed text letters given a braille sample stimulus in a matching-to-sample (MTS) format on the emergence of untrained (a) construction of print characters given braille samples, (b) construction of braille characters given print samples, (c) transcription of print characters given braille sample sentences, and (d) vocal reading given braille sample passages. The results demonstrated the generative development of these repertoires given MTS instruction.

A negative stimulus movement effect in pigeons

Rhesus monkeys and humans perform more accurately in matching-to-sample tasks when the sample stimulus moves through space (Washburn et al., 1989; Washburn, 1993). This Stimulus Movement Effect (SME) is believed to be due to movement increasing attention toward the sample stimulus, creating an easier discrimination between the sample and choice stimuli. To date, there is no evidence for this phenomenon in a non-mammalian species. In the current study, we investigate the possibility of an SME in an avian species. Across three experiments, pigeons were tested with moving and stationary sample stimuli in a non-matching- to-sample task. The area and velocity by which the sample stimulus traveled was manipulated but no advantage for moving over stationary sample trials was found within or across sessions. Even when a delay condition was implemented, there was no advantage for moving sample trials. Contrary to the results found in humans and monkeys, pigeons performed better when the sample was stationary, a negative SME, and no evidence was found that stimulus movement increases discrimination performance.

Unraveling sources of stimulus control in a temporal discrimination task.

In temporal discriminations tasks, more than one stimulus may function as a time marker. We studied two of them in a matching-to-sample task, the sample keylight and the houselight that signaled the intertrial interval (ITI). One group of pigeons learned a symmetrical matching-to-sample task with two samples (2s or 18s of a center keylight) and two comparisons (red and green side keys), whereas another group of pigeons learned an asymmetrical matching-to-sample task with three samples (2s, 6s, and 18s) and two comparisons (red and green). In the asymmetrical task, 6-s and 18-s samples shared the same comparison. In a subsequent retention test, both groups showed a preference for the comparison associated with the longer samples, a result consistent with the hypothesis that pigeons based their choices on the duration elapsed since the offset of the houselight (i.e., sample duration + retention interval). Results from two no-sample tests further corroborated the importance of the ITI illumination as a time marker: When the ITI was illuminated, the proportion of choices correlated positively with the retention interval; when the ITI was darkened, choices fell to random levels. However, the absolute value of choice proportions suggested that the sample stimulus was also a time marker. How multiple stimuli acquire control over behavior and how they combine remains to be worked out.

Computational Simulation of Equivalence Class Formation Using the go/no-go Procedure with Compound Stimuli.

Research about equivalence has commonly utilized human participants as experimental subjects. More recently, computational models have been capable of reproducing performances observed in experiments with humans. The computational model often utilized is called RELNET, and it simulates training and testing trials of conditional relations using the matching-to-sample procedure (MTS). The differentiation between sample stimulus and comparison stimuli, indispensable in MTS, implies operational difficulties for simulations. For this reason, new studies seek to utilize alternative procedures to MTS, which do not differentiate the functions of the antecedent stimuli. This work evaluated the possibility of developing a new computational model to simulate equivalence class formation using the go/no-go procedure with compound stimuli. In Experiment 1, artificial neural networks were utilized to simulate training of the AB and BC relations as well as the testing of the AC relation. The results showed that four out of six runs demonstrated equivalence class formation. Experiment 2 evaluated whether the additional class training performed in Experiment 1, which was analogous to the simulation of pre-experimental experience of human participants, would be essential for simulating the establishment of equivalence classes. It was found that it was not possible to simulate equivalence class formation without the additional class training. Altogether, the experiments show that it is possible to simulate equivalence class formation using the go/no-go procedure with compound stimuli and that it is necessary to conduct additional class training. The model developed is, therefore, an alternative to RELNET for the study of equivalence relations using computational simulations.

Emergence of Intraverbals with Antonyms Derived From Relations with Verbal and Nonverbal Stimuli

The present research studied the emergence of intraverbals with antonyms (e.g., “Name the opposite of empty”–“Full”) derived from learning skills with verbal and nonverbal stimuli. Five 3-year-old children learned to select the nonverbal comparison identical to a sample stimulus or of an opposite category from the sample, with a conditional discrimination procedure (e.g., selecting an empty cup in the presence of an empty cup when the contextual stimulus was “same” and selecting a full cup when the contextual stimulus was “opposite”). Then, an intraverbal probe related to these concepts was presented (e.g., “Name the opposite of empty”–“Full”). If the participant failed in the intraverbal probe, additional skills were taught or probed, and the intraverbal probe was repeated, which included conditional discriminations with more verbal stimuli than the initial conditional discrimination (e.g., selecting a full cup when told, “Point to the opposite of ‘empty’”). All 5 children demonstrated the emergence of most or all intraverbals. Two children received the sequence with a second stimulus set; they showed the emergence of intraverbals quicker than with the first stimulus set. Thus, the emergence of intraverbals after learning relations with nonverbal stimuli was demonstrated in young children. The identification of the skills present when the intraverbals emerged suggests that learning some of these skills is required for emergence, and they may be important to understand the emergence of verbal skills.

Short-term memory effects on visual global/local processing in tufted capuchin monkeys (Sapajus spp.).

Nonhuman primates, differently from humans, are less proficient at processing global properties of visual compound stimuli. It has been suggested that humans preferentially process stimuli globally because this enables a more economical encoding of the stimuli. In this study we assessed the role of short-term memory (STM) in global/local processing by presenting tufted capuchin monkeys with Navon-type hierarchical figures in both simultaneous and delayed matching-to-sample tasks. Capuchins' ability to discriminate hierarchical stimuli was evaluated as a function of increasing delay intervals (0.0, 0.5, 1.0, 2.0 and 3.0 sec) between the disappearance of the sample and the presentation of the comparison stimuli. The results showed that recognition accuracy for local features was above chance level with delays of up to 3.0 sec, as previously reported when capuchins were faced with nonhierarchical stimuli. By contrast, the recognition of global configurations was above chance level in simultaneous, 0.0 and 0.5 sec delay conditions but not at delay intervals of 1.0 sec or longer. These findings indicate that capuchins' propensity to process the local properties of visual stimuli can be observed when a delay is interposed between the presentation of sample and comparison stimuli and was not reversed by increasing the delay. Moreover, our results show that capuchins' local propensity was not reversed by increasing stimulus size. Overall, our study confirms crucial differences between human and nonhuman primates and adds new insights into the comparative research on visual grouping functions of these species. (PsycINFO Database Record

Decision-Making under Ambiguity Is Modulated by Visual Framing, but Not by Motor vs. Non-Motor Context. Experiments and an Information-Theoretic Ambiguity Model.

A number of recent studies have investigated differences in human choice behavior depending on task framing, especially comparing economic decision-making to choice behavior in equivalent sensorimotor tasks. Here we test whether decision-making under ambiguity exhibits effects of task framing in motor vs. non-motor context. In a first experiment, we designed an experience-based urn task with varying degrees of ambiguity and an equivalent motor task where subjects chose between hitting partially occluded targets. In a second experiment, we controlled for the different stimulus design in the two tasks by introducing an urn task with bar stimuli matching those in the motor task. We found ambiguity attitudes to be mainly influenced by stimulus design. In particular, we found that the same subjects tended to be ambiguity-preferring when choosing between ambiguous bar stimuli, but ambiguity-avoiding when choosing between ambiguous urn sample stimuli. In contrast, subjects’ choice pattern was not affected by changing from a target hitting task to a non-motor context when keeping the stimulus design unchanged. In both tasks subjects’ choice behavior was continuously modulated by the degree of ambiguity. We show that this modulation of behavior can be explained by an information-theoretic model of ambiguity that generalizes Bayes-optimal decision-making by combining Bayesian inference with robust decision-making under model uncertainty. Our results demonstrate the benefits of information-theoretic models of decision-making under varying degrees of ambiguity for a given context, but also demonstrate the sensitivity of ambiguity attitudes across contexts that theoretical models struggle to explain.