Adaptive coding of stimulus information in human fronto-parietal cortex during visual classification

Our ability to flexibly adapt to changing demands is supported by flexible coding of task-relevant information in frontal and parietal brain regions. Converging evidence suggest that coding of stimuli and task rules in these regions become stronger as task difficulty increases. Here, we tested whether there is a corresponding change in the representational format as well, an issue that has rarely been addressed directly in past research. Participants performed a visual classification task under varying levels of perceptual difficulty, while we acquired fMRI. Using a model-based representational similarity approach, we tested whether stimulus representations retain exemplar-level information. We expected representations to drop such exemplar-level information as perceptual difficulty increases, which would indicate a focus on representing behaviorally relevant category information. Counter to these expectations, and in contrast to previous research, we found frontal and parietal brain regions contained exemplar-level stimulus information. Interestingly, the anterior intraparietal sulcus (aIPS) retained exemplar-level stimulus information even in perceptually difficult trials, and these representations were directly related to performance. Overall, these findings call for a reassessment of the neural mechanisms underlying human adaptive behavior during visual classification.

Behavioural Features of Cerebral Visual Impairment Are Common in Children With Down Syndrome

It is widely recognised that children with Down syndrome have a broad range and a high prevalence of visual deficits and it has been suggested that those with Down syndrome are more likely to exhibit visual perception deficits indicative of cerebral visual impairment. This exploratory study aims to determine the prevalence of behavioural features suggestive of cerebral visual impairment (CVI) occurring with Down syndrome and whether the visual problems can be ascribed to optometric factors. A cohort of 226 families of children with Down syndrome (trisomy 21), aged 4–17, were invited to participate in a validated question inventory, to recognise visual perception issues. The clinical records of the participants were then reviewed retrospectively. A five-question screening instrument was used to indicate suspected CVI. The majority of the 81 families who responded to the questionnaire reported some level of visual perceptual difficulty in their child. Among this cohort, the prevalence of suspected CVI as indicated by the screening questionnaire was 38%. Only ametropia was found to have a significant association with suspected CVI, although this increased the correct prediction of suspected CVI outcome by only a small amount. Results suggest that children with Down syndrome are more likely to experience problems consistent with cerebral visual impairment, and that these may originate from a similar brain dysfunction to that which contributes to high levels of ametropia and failure to emmetropise. It is important that behavioural features of CVI are recognised in children with Down syndrome, further investigations initiated and appropriate management applied.

Perceptual Difficulty Persistently Increases Dominance in Binocular Rivalry—Even Without a Task

A major objective of perception is the reduction of uncertainty about the outside world. Eye-movement research has demonstrated that attention and oculomotor control can subserve the function of decreasing uncertainty in vision. Here, we ask whether a similar effect exists for awareness in binocular rivalry, when two distinct stimuli presented to the two eyes compete for awareness. We tested whether this competition can be biased by uncertainty about the stimuli and their relevance for a perceptual task. Specifically, we have stimuli that are perceptually difficult (i.e., carry high perceptual uncertainty) compete with stimuli that are perceptually easy (low perceptual uncertainty). Using a no-report paradigm and reading the dominant stimulus continuously from the observers’ eye movements, we find that the perceptually difficult stimulus becomes more dominant than the easy stimulus. This difference is enhanced by the stimuli’s relevance for the task. In trials with task, the difference in dominance emerges quickly, peaks before the response, and then persists throughout the trial (further 10 s). However, the difference is already present in blocks before task instruction and still observable when the stimuli have ceased to be task relevant. This shows that perceptual uncertainty persistently increases perceptual dominance, and this is magnified by task relevance.

Perceptual difficulty differences predict asymmetry in redundant modification with color and material adjectives

When referring to objects, speakers are often more specific than necessary for the purpose of establishing unique reference, e.g., by producing redundant modifiers. A computational model of referring expression production that accounts for many of the key patterns in redundant adjectival modification assumes that adjectives differ in how noisy (reliable), and consequently, how useful they are for reference. Here we investigate one hypothesis about the source of the assumed adjectival noise: that it reflects the perceptual difficulty of establishing whether the property denoted by the adjective holds of the contextually relevant objects. In Exp.1, we collect perceptual difficulty norms for items that vary in color and material. In Exp. 2, we test the highest (material) and lowest (color) perceptual difficulty items in a reference game and find that material is indeed less likely to be mentioned redundantly, replicating previous work. In Exp. 3, we obtain norms for the tested items in a second perceptual difficulty measure with the aim of testing the effect of perceptual difficulty within property type. The overall results provide preliminary support for the hypothesis that the propensity to redundantly use color over material adjectives may be driven by the relative ease of assessing an object’s color, compared to the relative difficulty of assessing its material.

The Prediction of Lado’s CAH in Taiwanese EFL Learners’ Perceptual Acquisition of /s/ and /θ/

This study mainly investigated the predictions of the Contrastive Analysis Hypothesis (CAH) on Taiwanese vocational high school EFL learners’ acquisition of two English fricative consonants (/s/ and /θ/) by examining the learners’ relative perceptual difficulty of the consonants. To achieve this purpose, two research questions were devised, and a self-designed listening identification test was carried out. A total of 43 students from a private vocational high school in northern Taiwan participated in this experiment. Their accuracy in perceiving the tested consonants was measured through the identification test. After all the participants’ test scores were gathered, an independent-samples t-test was used to analyze the data. The results of the study showed that the relative perceptual difficulty of the two fricatives for the students was /s/ = /θ/. The finding suggested that Lado’s (1957) CAH could not accurately predict the participants’ acquisition of the consonants in perception.

Cross-Situational Word Learning in Two Foreign Languages: Effects of Native Language and Perceptual Difficulty

Cross-situational word learning (CSWL) paradigms have gained traction in recent years as a way to examine word learning in ambiguous scenarios in infancy, childhood, and adulthood. However, no study thus far has examined how CSWL paradigms may provide viable learning pathways for second language (L2) word learning. Here, we used a CSWL paradigm to examine how native Australian English (AusE) speakers learned novel Dutch (Experiment 1) and Brazilian Portuguese (Experiment 2) word-object pairings. During each learning phase trial, two words and objects were presented without indication as to which auditory word belonged to which visual referent. The two auditory words formed a non-minimal or vowel minimal pair. Minimal pairs were classified as “perceptually easy” or “perceptually difficult” based on the acoustic-phonetic relationship between AusE and each L2. At test, participants again saw two visual referents but heard one auditory label and were asked to select the corresponding referent. We predicted that accuracy would be highest for non-minimal pair trials (in which the auditory words associated with the target and distractor object formed a non-minimal pair), followed by perceptually easy minimal pairs, with lowest accuracy for perceptually difficult minimal pair trials. Our results support these hypotheses: While accuracy was above chance for all pair types, in both experiments accuracy was highest for non-minimal pair trials, followed by perceptually easy and then perceptually difficult minimal pair trials. These results are the first to demonstrate the effectiveness of CSWL in adult L2 word learning. Furthermore, the difference between perceptually easy and perceptually difficult minimal pairs in both language groups suggests that the acoustic-phonetic relationship between the L1-L2 is an important factor in novel L2 word learning in ambiguous learning scenarios. We discuss the implications of our findings for L2 acquisition, cross-situational learning and encoding of phonetic detail in a foreign language.

Electroencephalogram-based Identification of Evidence Accumulation Stages in Decision-Making

Dating back to the 19th century, the discovery of processing stages has been of great interest to researchers in cognitive science. The goal of this article is to demonstrate the validity of a recently developed method, hidden semi-Markov model multivariate pattern analysis (HsMM-MVPA), for discovering stages directly from electroencephalographic data, in contrast to classical reaction-time-based methods. To test the validity of stages discovered with the HsMM-MVPA method, we applied it to two relatively simple tasks where the interpretation of processing stages is straightforward. In these visual discrimination electroencephalographic data experiments, perceptual processing and decision difficulty were manipulated. The HsMM-MVPA revealed that participants progressed through five cognitive processing stages while performing these tasks. The brain activation of one of those stages was dependent on perceptual processing, whereas the brain activation and the duration of two other stages were dependent on decision difficulty. In addition, evidence accumulation models (EAMs) were used to assess to what extent the results of HsMM-MVPA are comparable to standard reaction-time-based methods. Consistent with the HsMM-MVPA results, EAMs showed that nondecision time varied with perceptual difficulty and drift rate varied with decision difficulty. Moreover, nondecision and decision time of the EAMs correlated highly with the first two and last three stages of the HsMM-MVPA, respectively, indicating that the HsMM-MVPA gives a more detailed description of stages discovered with this more classical method. The results demonstrate that cognitive stages can be robustly inferred with the HsMM-MVPA.

EEG-based identification of evidence accumulation stages in decision making

Dating back to the 19th century, the discovery of processing stages has been of great interest to researchers in cognitive science. The goal of this article is to demonstrate the validity of a recently developed method, hidden semi-Markov model multivariate pattern analysis (HsMM-MVPA), for discovering stages directly from EEG data, in contrast to classical RT-based methods. To test the validity of stages discovered with the HsMM-MVPA method, we applied it to two relatively simple tasks where the interpretation of processing stages is straightforward. In these visual discrimination EEG experiments, perceptual processing and decision difficulty were manipulated. The HsMM-MVPA analysis revealed that participants progressed through five cognitive processing stages while performing these tasks. The brain activation of one of those stages was dependent on perceptual processing, while the brain activation and the duration of two other stages was dependent on decision difficulty. Additionally, evidence accumulation models (EAMs) were used to assess to what extent the results of HsMM-MVPA are comparable to standard RT-based methods. Consistent with the HsMM-MVPA results, EAMs showed that non-decision time varied with perceptual difficulty and drift rate with decision difficulty. Moreover, non-decision and decision time of the EAMs correlated highly with the first two and the last three stages of the HsMM-MVPA analysis, respectively, indicating that the HsMM-MVPA analysis gives a more detailed description of stages discovered with this more classical method. The results demonstrate that cognitive stages can be robustly inferred with the HsMM-MVPA analysis.