A hierarchy of cortical responses to sequence violations in three-month-old infants

The adult human brain quickly adapts to regular temporal sequences, and emits a sequence of novelty responses when these regularities are violated. These novelty responses have been interpreted as error signals that reflect the difference between the incoming signal and predictions generated at multiple cortical levels. Do infants already possess such a hierarchy of violation-detection mechanisms? Using high-density recordings of event-related potentials during an auditory local–global violation paradigm, we show that three-month-old infants process novelty in temporal sequences at two distinct levels. Violations of local expectancies, such as perceiving a deviant vowel “a” after repeated presentation of another vowel i-i-i, elicited an early auditory mismatch response. Conversely, violations of global expectancies, such as hearing the rare sequence a-a-a-a instead of the frequent sequence a-a-a-i, modulated this early mismatch response and led to a late frontal negative slow wave, whose cortical sources included the left inferior frontal region. These results suggest that the infant brain already possesses two dissociable systems for temporal sequence learning.     

Imitation: definitions, evidence, and mechanisms

Imitation can be defined as the copying of behavior. To a biologist, interest in imitation is focused on its adaptive value for the survival of the organism, but to a psychologist, the mechanisms responsible for imitation are the most interesting. For psychologists, the most important cases of imitation are those that involve demonstrated behavior that the imitator cannot see when it performs the behavior (e.g., scratching one's head). Such examples of imitation are sometimes referred to as opaque imitation because they are difficult to account for without positing cognitive mechanisms, such as perspective taking, that most animals have not been acknowledged to have. The present review first identifies various forms of social influence and social learning that do not qualify as opaque imitation, including species-typical mechanisms (e.g., mimicry and contagion), motivational mechanisms (e.g., social facilitation, incentive motivation, transfer of fear), attentional mechanisms (e.g., local enhancement, stimulus enhancement), imprinting, following, observational conditioning, and learning how the environment works (affordance learning). It then presents evidence for different forms of opaque imitation in animals, and identifies characteristics of human imitation that have been proposed to distinguish it from animal imitation. Finally, it examines the role played in opaque imitation by demonstrator reinforcement and observer motivation. Although accounts of imitation have been proposed that vary in their level of analysis from neural to cognitive, at present no theory of imitation appears to be adequate to account for the varied results that have been found.     

The neural correlates of statistical learning in a word segmentation task: An fMRI study

Functional magnetic resonance imaging (fMRI) was used to assess neural activation as participants learned to segment continuous streams of speech containing syllable sequences varying in their transitional probabilities. Speech streams were presented in four runs, each followed by a behavioral test to measure the extent of learning over time. Behavioral performance indicated that participants could discriminate statistically coherent sequences (words) from less coherent sequences (partwords). Individual rates of learning, defined as the difference in ratings for words and partwords, were used as predictors of neural activation to ask which brain areas showed activity associated with these measures. Results showed significant activity in the pars opercularis and pars triangularis regions of the left inferior frontal gyrus (LIFG). The relationship between these findings and prior work on the neural basis of statistical learning is discussed, and parallels to the frontal/subcortical network involved in other forms of implicit sequence learning are considered.     

Hebb repetition effects in visual memory: The roles of verbal rehearsal and distinctiveness

A version of the Hebb repetition task was used with faces to explore the generality of the effect in a nonverbal domain. In the baseline condition, a series of upright faces was presented, and participants were asked to reconstruct the original order. Performance in this condition was compared to another in which the same stimuli were accompanied by concurrent verbal rehearsal to examine whether Hebb learning is dependent on verbal processing. Baseline performance was also compared to a condition in which the same faces were presented inverted. This comparison was used to determine the importance in Hebb learning of being able to visually distinguish between the list items. The results produced classic serial position curves that were equivalent over conditions with Hebb repetition effects being in evidence only for upright faces and verbal suppression as having no effect. These findings are interpreted as posing a challenge to current models derived from verbal-domain data.     

Effects of interlimb practice on coding and learning of movement sequences

An interlimb practice paradigm was designed to determine the role that visual–spatial (Cartesian) and motor (joint angles, activation patterns) coordinates play in the coding and learning of complex movement sequences. Participants practised a 16-element movement sequence by moving a lever to sequentially presented targets with one limb on Day 1 and the contralateral limb on Day 2. Practice involved the same sequence with either the same visual–spatial or motor coordinates on the two days. A unilateral practice condition (control) was also tested where both coordinate systems were changed but the same limb was used. Retention tests were conducted on Day 3. Regardless of the order in which the limbs were used during practice, results indicated that keeping the visual–spatial coordinates the same during acquisition resulted in superior retention. This provides strong evidence that the visual–spatial code plays a dominant role in complex movement sequences, and this code is represented in an effector-independent manner.     

Choice both affects and reflects preferences

The free-choice paradigm is a widely used paradigm in psychology. It has been used to show that after a choice between two similarly pleasant stimuli, the pleasantness of the chosen one tends to increase, whereas the pleasantness of the rejected one tends to decrease—a spreading of alternatives. However, the methodological validity of the free-choice paradigm to study choice-induced preference change has recently been seriously questioned [Chen, K. M., & Risen, J. L. (2010). How choice affects and reflects preferences: Revisiting the free-choice paradigm. Journal of Personality and Social Psychology, 99, 573–594. doi:10.1037/a0020217]. According to this criticism, the classically reported spreading of alternatives between the first and second rating sessions cannot be unambiguously interpreted to reflect a true change in preferences and can be observed even for completely static preferences. Here, we used two measurement sequences, a classical Rating 1–choice–Rating 2 sequence and a control Rating 1–Rating 2–choice sequence, to disentangle the spreading of alternatives driven by the effect of choice from the artefactual effect highlighted by Chen and Risen. In two studies using different stimulus material (faces and odours), we find that choice has a robust modulatory impact on preferences for rejected odours, but not for chosen odours and not for faces.     

Effects of auditory rhythm on movement accuracy in dance performance

The present study addresses the impact of the rhythmic complexity of music on the accuracy of dance performance. This study examined the effects of different levels of auditory syncopation on the execution of a dance sequence by trained dancers and exercisers (i.e., nondancers). It was hypothesized that nondancers would make more errors in synchronizing movements with moderately and highly syncopated rhythms while no performance degradation would manifest among trained dancers. Participants performed a dance sequence synchronized with three different rhythm tracks that were regular, moderately syncopated, and highly syncopated. We found significant performance degradation when comparing conditions of no syncopation vs. high syncopation for both trained dancers (p = .002) and nondancers (p = .001). Dancers and nondancers did not differ in how they managed to execute the task with increasing levels of syncopation (p = .384). The pattern of difference between trained dancers and nondancers was similar across the No Syncop and Highly Syncop conditions. The present findings may have marked implications for practitioners given that the tasks employed were analogous to those frequently observed in real-life dance settings.     

Action sequences within and across hands: Evidence for hand-related sequence learning

Recent research into the acquisition of action sequences involving both hands suggests that the hand-related (sub)sequences are learned at least partly independently of one another. Here we investigated hand-related sequence learning with a novel approach. Eight stimuli were divided into two sets. Participants responded simultaneously to a pair of stimuli (one from each set) with keystrokes of both hands. The stimuli from one set appeared according to a probabilistic structure; no such structure was imposed on the other set of stimuli. The structured stimuli either were assigned to keystrokes of one hand only or were evenly distributed across keystrokes of both hands. Sequence learning was more pronounced under the within-hands assignment than under the across-hands assignment. This finding corroborates hand-related sequence learning and suggests that the executing hand constitutes a dimension that facilitates learning of sequential regularities among elements that pertain to this hand.     

Seeing the future: Natural image sequences produce “anticipatory” neuronal activity and bias perceptual report

This paper relates human perception to the functioning of cells in the temporal cortex that are engaged in high-level pattern processing. We review historical developments concerning (a) the functional organization of cells processing faces and (b) the selectivity for faces in cell responses. We then focus on (c) the comparison of perception and cell responses to images of faces presented in sequences of unrelated images. Specifically the paper concerns the cell function and perception in circumstances where meaningful patterns occur momentarily in the context of a naturally or unnaturally changing visual environment. Experience of visual sequences allows anticipation, yet one sensory stimulus also “masks” perception and neural processing of subsequent stimuli. To understand this paradox we compared cell responses in monkey temporal cortex to body images presented individually, in pairs and in action sequences. Responses to one image suppressed responses to similar images for ～500 ms. This suppression led to responses peaking 100 ms earlier to image sequences than to isolated images (e.g., during head rotation, face-selective activity peaks before the face confronts the observer). Thus forward masking has unrecognized benefits for perception because it can transform neuronal activity to make it predictive during natural change.     

The impact of training sequence and between-category similarity on unsupervised induction

Studies of supervised categorization often show better learning when examples are presented in random alternation rather than massed by category, but such interleaving impairs learning in unsupervised tasks. The exemplar comparison hypothesis explains this result by assuming that people in unsupervised tasks discover generalizations about categories by comparing individual examples, and that interleaving increases the difficulty of such within-category comparisons. The category invention hypothesis explains the interleaving effect by assuming that people are more likely to merge or aggregate potentially separable categories when they are interleaved, and this initial failure to recognize separate categories then acts as an effective barrier to further learning. The present experiments show that the interleaving effect depends on the similarity or alignability of the presented categories. This result provides evidence in favour of the category invention hypothesis, which expects that highly dissimilar (nonalignable) categories will resist aggregation and hence will not be affected by interleaving. The nonmonotonic pattern of learning, and the interaction between sequence and similarity, observed in the alignable conditions of Experiment 3 were also consistent with category invention, but not with exemplar comparison. Implications are discussed for real-world learning, especially the relationship between exposure and learning and between supervised and unsupervised learning.