John E. Richards, Department of Psychology, University of South Carolina.

Infants move visual attention in space without overtly moving their eyes. This is demonstrated in a spatial cueing procedure in which a cue occurs in one location, and a target occurs in the same location or a different location. The reaction time to move the eyes toward the target differs depending on the cue-target relation. A target in the same location of the cue facilitates localization of the target (“faciliation”) and the cue and target in different locations results in target localization at similar times as if no cue were present. However, if the time between the cue and target is lengthened, a target presented in the same location of the cue attenuates target localization (“inhibition of return”).
In several studies I have shown that the spatial cueing effects have corresponding changes in brain areas. This is studied by recording event-related potentials in EEG. The size of the ERP component occurring about 200 ms after target onset is larger for the cue-target shown in the same location. Cortical source analysis of the ERP component has localized this component to areas of the extrastriate cortex and the fusiform gyrus. This suggest that the brain areas are involved in spatial attention, and that the enhancement of the brain area is partially responsible for the behavioral effects.

The purpose of the current study is to examine the relation of these spatial cueing effects to central attention. The level of sustained attention can be assessed by measuring heart rate changes (HR deceleration) occurring to the central stimulus. I expect that when children are attending to the central stimulus that the infant’s responsiveness to any stimulus is enhanced. Thus I expect to find the spatial cueing effects (facilitation, inhibition of return) to be largest when sustained attention to the central stimulus is occurring. This experiment also will use cortical source localization of the ERP effects and will show how attention to the central stimulus affects brain areas known to be important in the development of infant spatial attention.

Brittany M. Mallin & John E. Richards, Dept. of Psychology, University of South Carolina.

Currently, we are investigating the effect of the presence of a central stimulus on saccadic localization of a peripheral stimulus. Traditional studies in this area have used simple black and white geometric stimuli to show that attention to a focal stimulus attenuates localization of a peripheral stimulus. A prior study by Mallin & Richards (submitted) found that the nature of complex and dynamically-changing stimuli and attention affected the latency to localize peripheral stimuli. The goals of the present study were: 1) to control audio and visual components in construction of movement conditions using complex and dynamically-changing stimuli, 2) to implement a new addition condition, more similar to prior research using simple, black and white stimuli, made up of scenes in which a silent new character was added in a different location, 3) to examine heart rate changes and stimulus movement together, so peripheral stimulus localization could occur during attention or inattention. Infants at 14, 20 and 26 weeks of age were presented with scenes from a “Sesame Street” movie until fixation on a moving character occurred, and then presented with scenes in which the character movement occurred in a new location. The electrocardiogram (ECG) was recorded and heart rate changes were used to define attention phases. For 20-wk-old infants, localization of the peripheral stimulus was faster when infants were attentive than when inattentive for scenes in which the character moved from one location to another and for scenes in which movement and sound shifted from one character to another. For both age groups localization of the peripheral character was slower during attention when the first character disappeared and a new character appeared in a different location, as previously found. The new addition condition also elicited this result. Interestingly, for 20-wk-old infants, overall reaction times were faster in conditions where the initial character moved or was replaced, that is no character remained in the initial location. Upon examination of the main sequence relationship, we found that there was a decreased slope for 20-wk-olds and a larger slope for 26-wk-olds while engaged in attention. We also found a significantly larger main sequence slope for the new addition condition, characterized by an initial stimulus that continues to move when the peripheral stimulus is presented, compared to the shift condition, where movement of the first stimulus stops upon presentation of the peripheral stimulus. These results partially replicate prior findings showing that attention to a focal stimulus affects localization of peripheral stimuli, but suggest that the nature of the stimuli being localized modifies the role of attention in affecting eye movements to peripheral stimuli.

Our current studies in this area use this presentation procedure to examine the effect of changing auditory and visual information. Infants are presented with complex, dynamically changing, audio-visual, figures extracted from Sesame Street movies. The stimuli are presented in one location until the infant is looking. Then the audio and visual components of the stimulus are changed independently, and shown in the first or second location. With this procedure we can distinguish the separate effects of localizing a changing audio-visual stimulus, changing auditory stimulus, or changing visual stimulus. The effects of stimulus modality on the localization of peripheral stimuli may be independently examined.

John E. Richards, Department of Psychology, University of South Carolina

A task that is closely related to brain activity is the prosaccade-antisaccade task. A stimulus is presented in the center and then a target is presented in the periphery. Depending on the instructions, or cues, or central stimulus, the participant moves their eyes toward the target (prosaccade) or away from the target to the opposite side (antisaccade). I have shown in two studies that attention cueing (spatial cues) and movement cues (type of movement) will facilitate the latency of the eye movement toward the appropriate location. Attention cueing is accompanied by enhanced activities in brain areas associated with spatial attention (e.g., extrastriate occipital cortex), whereas movement cueing enhances brain areas associated with eye movement control (frontal eye fields; prefrontal cortex; frontal pole).

Currently, I am doing a study with adolescents. During adolescence there are differential rates of development of the brain areas associated with attention cueing and movement cueing. The occipital cortex seems to develop to adult levels of functioning more quickly than frontal cortex. This differential development is seen most strongly during adolescence when prefrontal cortex and associated voluntary control shows more rapid development. The current study tests children from age 10 to 18, and college-age participants, in a prosaccade-antisaccade task. I expect to find changes in the eye movement latencies across this age range that are closely associated with brain area, differential effect of cueing on eye movement latency, and differential brain activity depending on cueing type.

Michael L. Stevens & John E. Richards, Department of Psychology, University of South Carolina.

The purpose of this study is to examine the effect of central stimulus comprehensibility on attention in children ranging from 6 months to 2 years. This will be done by using distractors presented at a priori HR-look duration combination intervals. The central stimulus will be a Sesame Street movie, “Follow that Bird,” and language comprehensibility will be modified by having versions with English, Spanish, Low-Pass filtered, or reverse speech. The distractors will be computer-generated abstract visual patterns or another Sesame Street movie (“Sesame Street 25th Anniversary”) presented on adjacent TV on the right or left of the center television monitor. The distractors will be presented at times defined by the duration of the look at distractor onset and by HR-defined attention phases. The goal of the study is to examine the effect of central stimulus language comprehensibility on the latency and probability of distractor latency as a function of time-HR defined delays.

We are also testing a group of infants at 2 years of age. Some of the preliminary analyses of the first study have shown that attention is engaged equally by movie presentations with English and Spanish soundtracks, but that filtered or reverse speech do not engage attention. That is, infants are more easily distracted from viewing the center stimulus when the filtered or reverse speech movie is shown than when the English or Spanish soundtracks are shown. This difference is paralleled by minimal heart rate change to the former stimuli and large HR changes to the latter stimuli. We are now replicating this effect in 2-year-old children with a variety of stimuli (English, Spanish, Arabic, Chinese, older-child TV program, uninteresting TV program, computer-generated audiovisual stimuli).

Greg D. Reynolds, Department of Psychology, Appalachian State University
John E. Richards, Department of Psychology, University of South Carolina

The modified-oddball paradigm has been used to measure ERP components associated with attention and recognition memory in infancy. Infants are familiarized with 2 stimuli and then exposed to brief presentations of three types of memory stimuli: frequent familiar, infrequent familiar, and infrequent novel. Recognition memory is inferred based on differential cortical responding to each of the memory stimulus types. A middle-latency negative ERP component over central leads labeled Negative Central (Nc) is assumed to reflect a general orienting response associated with attention. The Nc has been found to be greater in amplitude following novel stimulus presentations. Late slow waves proposed to reflect recognition memory include the negative slow wave (associated with novelty detection), and the positive slow wave (associated with an updating of recognition memory). A commonly used behavioral measure of recognition memory is the visual paired-comparison choice trial. Paired-comparison trials involve simultaneous presentation of a familiar and a novel stimulus. Recognition memory for the familiar stimulus is inferred when infants spend a greater proportion of time looking at the novel stimulus (i.e., demonstrate a novelty preference). No study to date has measured ERPs during paired-comparison trials because of the eye-movement artifacts produced during shifts between stimuli. One goal of the present study was to examine infant ERPs during paired-comparison trials by utilizing independent components analysis to identify and remove eye-movement components from the EEG data. A second goal was to examine the consistency between ERP components and behavioral correlates of attention and recognition memory by embedding paired-comparison trials within the modified-oddball paradigm.

Infants 20, 26, and 32 weeks of age served as participants. Infants were familiarized with two stimuli prior to testing. Participants were then exposed to alternating blocks of paired-comparison trials and brief stimulus presentations. The paired-comparison trials and blocks of brief stimulus presentations were alternated in order to measure the infants’ visual preferences as the study progressed. Look durations during the paired-comparison trials were scored off-line to obtain novelty preference scores. Electroencephalographic recordings were made with a 126-channel system and ERP averages were made from -50 ms to 2000 ms around stimulus onset for brief stimulus exposures, and for the duration of the paired-comparison trials. Our ERP analysis focused on the Nc component.

There was a significant effect of age on visual preference. The 26- and 32-week-olds preferred novel stimuli, whereas the 20-week-olds preferred familiar stimuli. In the ERP analysis of paired-comparison trials, greater amplitude Nc was found to the non-preferred stimulus. When infants demonstrated a novelty preference, Nc was greater in amplitude to the familiar stimulus (and vice versa). Results of the ERP analysis of brief stimulus presentations replicated past studies with greater amplitude Nc following novel stimulus presentations. These findings indicate that behavioral measures can be successfully integrated into ERP studies of infant cognitive development, although ERP and behavioral findings may not be entirely consistent. While infants demonstrated greater amplitude Nc to novel stimuli following brief stimulus presentations, greater amplitude Nc was found to familiar stimuli when look duration was indicative of a novelty preference.

Our current studies in this area use this mixed presentation procedure. Infants are presented with paired-comparison trials interspersed with brief presentations. The presentation sequence is designed to elicit preferential looking to a novel or familiar stimulus. In one study stimulus familiarity is elicited by repeated presentations of one stimulus, and the second stimulus changes on each trial. In a second study we are using familiar or novel toys, and mother or stranger faces. With this procedure we can examine the brain correlates of familiarity and novelty preference.

John E. Richards, Department of Psychology, University of South Carolina

Brain activity generates electrical potentials that may be recorded on the scalp, the “electroencephalogram” (EEG). Ongoing EEG can be modified by psychophysiological experiments requiring cognitive activity. When events are time-locked to the EEG recording the “event-related potential” (ERP) is measured. The ERP is thought to reflect activity of the brain in areas that control the cognitive processes involved in the psychophysiological tasks. A quantitative technique called “cortical source analysis” can identify the brain areas that are the source of the electrical activity recorded on the scalp, and by inference, the areas of the brain involved in the cognitive processes. Cortical source analysis has used simple models of brain topography and impedance in order to simply calculations for this analysis, e.g., multi-sphere models. However, realistic models of the media inside the head (gray matter, white matter, skull, scalp, CSF, dura) may be used in order to do cortical source analyses. These realistic models give more accurate locations of the sources inside the head, realistic calculation of the topography of the resistances in head media, and whole field electrical calculations of the effect of the cortical sources on the electrical activity on the scalp. We have used these models in a limited way with infant participants doing attention and recognition memory tasks; one of use (JER) has used these models successfully with adult and adolescent participants.

Our current work in this area involves the development of models for realistic cortical source in infant participants. These models demand that anatomical MRIs be done on infant participants. In one scenario an individual infant has the anatomical MRI and then participates in psychophysiological experiments. The MRI then can be used as a realistic model of the media inside the head and cortical source analysis of the resulting ERP data in the psychophysiological experiment is more accurately done. We currently are working on developing recording protocols for infant MRIs in order to pursue this work. A second scenario is to have a library of anatomical MRIs in order to use a infant head that is of similar shape to an infant being tested in a psychophysiological experiment. A third scenario is the development of a stereotaxic atlas (e.g., Talairach atlas; MNI atlas). The latter two scenarios will be examined both with MRIs recorded in our laboratory, and in conjunction with the library of MRIs being recorded in the NIH MRI Study of Brain Development.

Several complications are being examined. First, the resistance values of the media inside infant’s heads are not known. Bone density values are much smaller in infant participants, and skin / scalp have fewer dead cells, leading to less resistance in these media in infants in adults. Second, infants have places in the skull where the bones are not yet joined (seams, fontanel). This leads to current leakage to the recording electrodes on the scalp. Third, the overall topography of the brain-skull relation differs in infants and adults, and individual anatomical areas (e.g., Brodmann areas) have a different relation to external skull landmarks in infants and adults. Fourth, the lack of axonal myelination in the first few months and changes in myelination over childhood affect the degree to which cell bodies and axons can be differentiated. So called “gray matter” in adults and adolescents primarily consists of cell bodies and “white matter” are myelinated axons. In the infant however, gray matter consists of both cell bodies and axons. These complications are being evaluated in the development of realistic models of the head for cortical source analysis of infant EEG and ERP.