Application of EEG,ERP and intracranial recordings to the investigation of cognitive functions in children

Neurophysiological measures can provide important information about the substrate of cognitive function in children, and most importantly, can give precise temporal information about ‘on‐line’ brain function. These measures can be readily used in infants and children, and we present some examples of their application to understanding cognitive development. The most widely used of these techniques for developmental research is the method of event‐related potentials (ERPs). In addition, the electroencephalogram (EEG) and the more rarely used invasive, intracranial investigations are also important to furthering our knowledge of how the brain–behaviour relations develop. The paper summarizes practical issues and presents some selected examples of experimental and clinical research.     

The effect of witnessing consequences on the behavioral recordings of experimental observers

The cueing effects of interviewer praise contingent on a target behavior and expectation of behavior change were examined with six observers. Experiment I investigated the effect of cues in conjunction with expectation. Experiment II assessed the relative contributions of cues and expectation, and Experiment III examined the effect of cues in the absence of expectation. The frequencies of two behaviors, client eye contact and face touching, were held constant throughout a series of videotaped interviews between an "interviewer" and a "client". A within-subjects design was used in each experiment. During baseline conditions, praise did not follow eye contact by the client on the videotape. In all experimental conditions, praise statements from the interviewer followed each occurrence of eye contact with an equal number of praises delivered at random times when there was no eye contact. Three of the six observers dramatically increased their recordings of eye contact during the first experimental phase, but these increases were not replicated in a second praise condition. There were no systematic changes in recorded face touching. Witnessing the delivery of consequences, rather than expectation seemed to be responsible for the effect. This potential threat to the internal validity of studies using observational data may go undetected by interobserver agreement checks.     

From single-channel recordings to brain-mapping devices: the impact of electroencephalography on experimental psychology

Since its discovery in 1920, the electroencephalogram (EEG) has become a widely used tool in experimental psychology. Although originally the merits of the method were seen first of all in an improvement of medical diagnostics it was soon understood by psychologists that EEG can also be used to study psychic processes in healthy participants. This article summarizes important events in the history of EEG research that laid the ground for this development, as fast Fourier transformation to analyze the spontaneous activity and signal averaging to improve the signal-to-noise ratio. The article shows how general technological developments were the prerequisite for these methodological improvements in EEG research and how they inspired new research questions. Key discoveries that proved unequivocally that psychic processes do become manifest in EEG signals are briefly reviewed, and the emerging paradigm of cognitive psychophysiology, which is closely linked to the development of EEG research, is described.     

Visual feedback of hand trajectory and the development of infant prehension

The purpose of this longitudinal infant study was to investigate the influence of visual information of the hand trajectory in the development of reaching movements in prehension. Ten infants were observed biweekly from the age of 10 weeks to 28 weeks and 1 yr. The reach kinematics were analyzed at age of reach onset, 6 mo and 1 yr of age. The results showed that infants reached for objects earlier when the visual feedback of the hand trajectory and the object were available. However, visual feedback of the hand trajectory did not change the movement speed and smoothness of the reach component at 6 mo and 1 yr of age. Infants reached for the larger object earlier and with higher velocity than for the smaller object. Visual feedback of the hand facilitates the age of reaching onset, but when the reaching movements become sufficiently stable, infants perform equally well with or without visual trajectory feedback of the hand.     

Reproducibility and a unifying explanation: Lessons from the shape bias

The goal of science is to advance our understanding of particular phenomena. However, in the field of development, the phenomena of interest are complex, multifaceted, and change over time. Here, we use three decades of research on the shape bias to argue that while replication is clearly an important part of the scientific process, integration across the findings of many studies that include variations in procedure is also critical to create a coherent understanding of the thoughts and behaviors of young children. The “shape bias,” or the tendency to generalize a novel label to novel objects of the same shape, is a reliable and robust behavioral finding and has been shown to predict future vocabulary growth and possible language disorders. Despite the robustness of the phenomenon, the way in which the shape bias is defined and tested has varied across studies and laboratories. The current review argues that differences in performance that come from even seemingly minor changes to the participants or task can offer critical insight to underlying mechanisms, and that working to incorporate data from multiple labs is an important way to reveal how task variation and a child’s individual pathway creates behavior—a key issue for understanding developmental phenomena.     

An experimental analysis of the cost of food in a closed economy.

Rats lived in individual chambers in which the only food available was delivered for lever pressing. During Stage I, a fixed number of presses was required for each food pellet. As this fixed ratio of presses per food pellet was increased daily, a rat's daily intake of food was reduced. During Stage II, the cost of a food pellet was increased by replacing each fixed ratio with its interval equivalent. Each interval was a rat's mean time between the first press of a ratio and the delivery of a pellet during Stage I. During Stage II, only two presses were every required for a food pellet: The first press initiated a delay and the second activated the pellet dispenser after that delay elapsed. Food intakes for the series of fixed ratios and a rat's series of delay equivalents were very similar when plotted as a function of delay, but not when plotted as a function of presses per pellet. Consequently, the fixed ratio reduced food intake because larger ratios increased delay to food from the first press of a ratio. Observations and an analysis of interresponse times further revealed that as the fixed ratio increased, and local as well as overall rate of food intake decreased, lever pressing became more stereotyped. Because this increased stereotypy resulted in greatly increased rates of lever pressing, delay to food was minimized, and perhaps more importantly, so too was the reduction of a rat's baseline daily intake.     

The role of sight of the hand in the development of prehension in childhood

In two studies, children between 5 and 10 years of age were asked to reach to grasp an object without sight of the hand during the movement. The oldest children and adults were faster when they could see the hand and increased maximum grip aperture when they could not see the hand. The 10-year-olds were less able to integrate grasp and lift than adults when they could see their hands. Children aged 5 and 6 showed no increase in movement time when they could not see the hand and did not adapt maximum grip aperture to lack of sight. These effects remained when children were encouraged to reach for and lift the target as quickly as possible. The results indicate that younger children did not give preference to vision in the control of prehension, while older children used visual feedback to improve efficiency. Dependence on sight of the hand for the control of prehension does not simply decrease with age, but it may be integrated into an anticipatory control strategy where it contributes to the efficiency of control.     

Percepts to recollections: insights from single neuron recordings in the human brain

Transformation of experience into memories that can guide future behavior is a common ability across species. However, only humans can declare their perceptions and memories of experienced events (episodes). The medial temporal lobe (MTL) is central to episodic memory, yet the neuronal code underlying the translation from sensory information to memory remains unclear. Recordings from neurons within the brain in patients who have electrodes implanted for clinical reasons provide an opportunity to bridge physiology with cognitive theories. Recent evidence illustrates several striking response properties of MTL neurons. Responses are selective yet invariant, associated with conscious perception, can be internally generated and modulated, and spontaneously retrieved. Representation of information by these neurons is highly explicit, suggesting abstraction of information for future conscious recall.     

Abstract levels of motor control in prehension: Normal and pathological performance

Voluntary motor pattern generation is typically assumed to be organized hierarchically, with an abstract (effector independent) upper level which constrains the lower levels. There are at least two advantages of such an organization: it allows the system to exploit its redundancy, and when controlling a very large number of degrees of freedom the burden of control can be distributed over a sequence of stages. Experiments are reviewed which provide a consistent body of evidence in support of the contention that there is an effector independent level of motor representation in prehension. This is consistent with a hierarchically organized motor pattern generator. One set of experiments demonstrated that during active movement of a hand-held load, the coupling of grip force with movement induced load force is independent of how the load is grasped or how it is actively moved. A second set of experiments demonstrated that the movement patterns observed during reach-to-grasp are preserved over changes in the effector system used. Extensions and replications of these experiments with Parkinson's patients illustrates the idea that neurological problems may affect different levels of the control hierarchy suggesting that these levels may be anatomically as well as functionally distinguishable.PsycINFO classification: 2330; 2520; 3297     

Grasping a better understanding of the intrinsic dynamics of rhythmical and discrete prehension

In this study, the authors examined the influence of the intrinsic dynamics of discrete and rhythmical prehension. Six adults underwent a scaling procedure in which the movement time was systematically increased so that it corresponded with 6 frequencies: 0.5, 0.75, 1.0, 1.25, 1.5, and 1.75 Hz. In posttests, participants moved at their own preferred pace. No differences were found in the relative time to final hand closure (T[rfc]) between the rhythmical and discrete conditions. The variability of T[rfc] was shown to be less at the preferred step of scaling than during the posttest. With the scaling technique, one can guide participants into more stable movement patterns than they can achieve when the metronome is not present, because, when the metronome is present, their movements become anchored to the external pacing cue. Those findings provide support for the use of a scaling technique to identify the influence of the intrinsic dynamics during rhythmical and discrete movements.     

Techniques for the production of point-light and fully illuminated video displays from identical recordings

Illumination of only a few key points on a moving human body or face is enough to convey a compelling perception of human motion. A full understanding of the perception ofbiological motion from point-light displays requires accurate comparison with the perception of motion in normal, fully illuminated versions of the same images. Traditionally, these two types of stimuli (point-light and fully illuminated) have been filmed separately, allowing the introduction of uncontrolled variation across recordings. This is undesirable for accurate comparison of perceptual performance across the two types of display. This article describes simple techniques, using proprietary software, that allow production of point-light and fully illuminated video displays from identical recordings. These techniques are potentially useful for many studies of motion perception, by permitting precise comparison of perceptual performances across point-light displays and their fully illuminated counterparts with accuracy and comparative ease.     

Thinking ahead: the case for motor imagery in prospective judgements of prehension

How similar are judgements concerning how we expect to perform an action, to how we actually behave? The veracity of such prospective action judgements, and the mechanisms by which they are computed, was explored in a series of tasks that involved either grasping (MC conditions) or thinking about grasping (PJ conditions) a dowel presented in various orientations. PJs concerning limits of comfortable hand supination and pronation when turning a dowel in the picture plane were highly consistent with values obtained during actual hand rotation (Exp. 1). The same was true for judgements regarding the level of awkwardness involved in adopting a prescribed grip (e.g. overhand with right hand) for dowels in various picture plane orientations (Exp. 2). When allowed to select the most natural grip (overhand versus underhand) or hand (left versus right) for engaging dowels in these orientations, subjects preferred virtually identical responses in both PJ and MC conditions. In both instances, they consistently chose the least awkward response options. As would be expected for actual movements, PJs involving awkward hand postures had longer response times (RTs), and were less accurate. Likewise, latencies for both grip and hand judgements tended to increase as a function of the angular distance between the current positions of subjects' hands, and the orientation of the chosen posture. Together, these findings are consistent with a the hypothesis that PJs involve mentally simulated actions, or motor imagery. These results suggest that motor imagery does not depend on the existence of a completed premotor plan (Jeannerod, 1994), but may instead be involved in the planning process itself. A provisional model for the involvement of imagery in motor planning is outlined, as are a set of criteria for evaluating claims of the involvement of motor imagery in problem solving.     

The effects of a pre-movement delay on the kinematics of prehension in middle childhood

The present study examined the effects of a pre-movement delay on the kinematics of prehension in middle childhood. Twenty-five children between the ages of 5 and 11 years made visually open-loop reaches to two different sized objects at two different distances along the midline. Reaches took place either (i) immediately, or (ii) 2 s after the occlusion of the stimulus. In all age groups, reaches following the pre-movement delay were characterised by longer movement durations, lower peak velocities, larger peak grip apertures and longer time spent in the final slow phase of the movement. This pattern of results suggests that the representations that control the transport and grasp component are affected similarly by delay, and is consistent with the results previously reported for adults. Such representations therefore appear to develop before the age of 5.     

Color spaces of color-normal and color-abnormal observers reconstructed from response times and dissimilarity ratings

With multidimensional scaling analysis, color spaces were reconstructed from reaction times (RTs) required to make same-different judgements of pairs of 15 equiluminant colors and from dissimilarity ratings between them. In addition to normal trichromats, observers with red-green color deficiency were tested. Two main purposes were served by this study: (1) to compare spatial representations of colors derived from discriminative RTs with those derived from dissimilarity measures and (2) to examine whether the task may selectively affect the dimension reflecting, in color-abnormal spaces, the deficient red-green mechanism. Contradicting our hypothesis of lower dimensionality of RT spaces, as compared with rating spaces, no consistent differences in solution dimensionality were found. However, configurations derived from the two measures diverged. The rating procedure yielded the most logical results for recovering color space. The RT configuration revealed contraction in the tritanopic direction, indicating longer color processing when the short-wavelength mechanism is involved, and in addition, for color-abnormal observers, clustering in the protanopic and deuteranopic directions, indicating even longer processing by the deficient red-green mechanism. This finding implies that RTs are suitable for detecting temporal differences in color processing but, for that very same reason, rather ill-suited for reconstructing color spaces.     

An experimental comparison of stimulus and response translated power functions for brightness

A threshold parameter has been introduced into the power law in two different ways, one involving, translation on the stimulus axis (the Ф-Law) and the second involving translation on the response axis (the Ψ-Law). In this study the two laws were compared using the data from 6 Ss making magnitude estimation judgments of brightness. Although the prevalent view appears to favor the Ф -Lau, the data of this study clearly dictate a choice of the Ψ-Law over the $-Law for brightness.     

Coordination dynamics of rhythmical and discrete prehension movements: Implications of the scanning procedure and individual differences

The aim of this study was to compare the coordination dynamics of discrete and rhythmical reaching and grasping movements from a dynamical systems perspective. Previous research from this theoretical perspective had focused on rhythmical actions and it is unclear to what extent discrete movements are amenable to a similar dynamical systems analysis. Six adult subjects performed prehension in two conditions: a discrete, non-continuous mode and a rhythmical, continuous mode. A `scanning procedure' was implemented between pre- and post-tests in which the required time of final relative hand closure (T_rfc) was systematically varied. It was shown that the error in the reaching and grasping pattern was least at an attractor region and systematically increased with deviation from the attractor. Results also indicated that there were no differences between condition or trial block for the group. However, there were several within-subject effects of interest. The validity of the scanning procedure was found to be questionable in the discrete condition, where four subjects showed differences in T_rfc between pre- or post-test and the predicted T_rfc of the scanning procedure. Four out of six subjects also had different preferred T_rfc values for discrete and rhythmical movement, indicating that individual specific models might need to be constructed for future dynamical modelling of discrete movement.PsycINFO classification: 2330