The Effects of Repeated Testing, Simulated Malingering, and Traumatic Brain Injury on Visual Choice Reaction Time.

Choice reaction time (CRT), the time required to discriminate and respond appropriately to different stimuli, is a basic measure of attention and processing speed. Here, we describe the reliability and clinical sensitivity of a new CRT test that presents lateralized visual stimuli and adaptively adjusts stimulus onset asynchronies using a staircase procedure. Experiment 1 investigated the test-retest reliability in three test sessions performed at weekly intervals. Performance in the first test session was accurately predicted from age and computer-use regression functions obtained in a previously studied normative cohort. Central processing time (CentPT), the difference between the CRTs and simple reaction time latencies measured in a separate experiment, accounted for 55% of CRT latency and more than 85% of CRT latency variance. Performance improved significantly across the three test sessions. High intraclass correlation coefficients were seen for CRTs (0.90), CentPTs (0.87), and an omnibus performance measure (0.81) that combined CRT and minimal SOA z-scores. Experiment 2 investigated performance in the same participants when instructed to feign symptoms of traumatic brain injury (TBI): 87% produced abnormal omnibus z-scores. Simulated malingerers showed greater elevations in simple reaction times than CRTs, and hence reduced CentPTs. Latency-consistency z-scores, based on the difference between the CRTs obtained and those predicted based on CentPT latencies, discriminated malingering participants from controls with high sensitivity and specificity. Experiment 3 investigated CRT test performance in military veterans who had suffered combat-related TBI and symptoms of post-traumatic stress disorder, and revealed small but significant deficits in performance in the TBI population. The results indicate that the new CRT test shows high test-retest reliability, can assist in detecting participants performing with suboptimal effort, and is sensitive to the effects of TBI on the speed and accuracy of visual processing.

The Effects of Repeat Testing, Malingering, and Traumatic Brain Injury on Computerized Measures of Visuospatial Memory Span.

Spatial span tests (SSTs) such as the Corsi Block Test (CBT) and the SST of the Wechsler Memory Scale are widely used to assess deficits in spatial working memory. We conducted three experiments to evaluate the test-retest reliability and clinical sensitivity of a new computerized spatial span test (C-SST) that incorporates psychophysical methods to improve the precision of spatial span measurement. In Experiment 1, we analyzed C-SST test-retest reliability in 49 participants who underwent three test sessions at weekly intervals. Intraclass correlation coefficients (ICC) were higher for a psychophysically derived mean span (MnS) metric (0.83) than for the maximal span and total correct metrics used in traditional spatial-span tests. Response times (ReTs) also showed high ICCs (0.93) that correlated negatively with MnS scores and correlated positively with response-time latencies from other tests of processing speed. Learning effects were insignificant. Experiment 2 examined the performance of Experiment 1 participants when instructed to feign symptoms of traumatic brain injury (TBI): 57% showed abnormal MnS z-scores. A MnS z-score cutoff of 3.0 correctly classified 36% of simulated malingerers and 91% of the subgroup of 11 control participants with abnormal spans. Malingerers also made more substitution errors than control participants with abnormal spans (sensitivity = 43%, specificity = 91%). In addition, malingerers showed no evidence of ReT slowing, in contrast to significant abnormalities seen on other malingered tests of processing speed. As a result, differences between ReT z-scores and z-scores on other processing speed tests showed very high sensitivity and specificity in distinguishing malingering and control participants with either normal or abnormal spans. Experiment 3 examined C-SST performance in a group of patients with predominantly mild TBI: neither MnS nor ReT z-scores showed significant group-level abnormalities. The C-SST improves the reliability and sensitivity of spatial span testing, can accurately detect malingering, and shows that visuospatial working memory is largely preserved in patients with predominantly mild TBI.

Intermodal attention modulates visual processing in dorsal and ventral streams.

Attending to visual objects while ignoring information from other modalities is necessary for performing difficult visual discriminations, but it is unclear how selecting between sensory modalities alters processing within the visual system. We used an audio-visual intermodal selective attention paradigm with fMRI to study the effects of visual attention on cortical activity in the absence of competitive interactions between multiple visual stimuli. Complex stimuli (faces and words) activated higher visual areas even in the absence of visual attention. These stimulus-dependent activations (SDAs) covered foveal retinotopic cortex, extended ventrally to the anterior fusiform gyrus and dorsally to include multiple distinct foci in the intraparietal sulcus (IPS). Attention amplified the baseline response in posterior retinotopic regions and altered activity in different ways in the extrastriate dorsal and ventral pathways. The majority of the IPS was strongly and exclusively activated by visual attention: attention-related modulations (ARMs) encompassed and spread well beyond the focal SDAs. In contrast, in the fusiform gyrus only a small subset of the regions activated by unattended stimuli showed ARMs. Ventral cortex was also heterogeneous: we found a distinct ventrolateral region in the occipitotemporal sulcus (OTS) that was activated exclusively by attention, showing neither SDAs nor any significant stimulus preferences. Attention-dependent activations in the IPS and the OTS suggest that these regions play critical roles in intermodal visual attention.

Efficacy of tailored computer-based neurorehabilitation for improvement of movement initiation in Parkinson's disease.

While Parkinson's disease (PD) is considered a motor disorder, motor signs of PD can be exacerbated by cognitive dysfunction. We evaluated the efficacy of a computer-based cognitive rehabilitation training program designed to improve motor-related executive function. Thirty people with PD and 21 controls participated in the 10-day training. Training consisted of a two-phase button press task. First, subjects produced an externally cued (EC) digit sequence, typing numbers displayed on the computer screen. Second, subjects were prompted to generate the same sequence in the absence of the number display (internally represented sequence, IR). Sequence length was automatically adjusted to maintain 87% correct performance. Participants were evaluated before and after training using a fixed version of the training task, and generalization of training was assessed using measures involving IR motor sequencing, switching and activities of daily living. PD participants were divided into two groups, those who showed impairment in IR motor sequence production prior to training (N=14) and those whose performance was similar to controls (N=16). Following training the impaired PD group showed significantly greater reduction in sequence initiation and completion time and in error rate for IR conditions compared to the unimpaired PD and control groups. All groups improved on Trails B-A, and pre-training Trails B was identified as a predictor of training-based improvement in IR sequence completion time and error rate. Our findings highlight the importance of neurorehabilitation tailored to the specific cognitive deficits of the PD patient.

Computerized analysis of error patterns in digit span recall.

We analyzed error patterns during digit span (DS) testing in four experiments. In Experiment 1, error patterns analyzed from a community sample of 427 subjects revealed strong primacy and recency effects. Subjects with shorter DSs showed an increased incidence of transposition errors in comparison with other error types and a greater incidence of multiple errors on incorrect trials. Experiment 2 investigated 46 young subjects in three test sessions. The results replicated those of Experiment 1 and demonstrated that error patterns of individual subjects were consistent across repeated test administrations. Experiment 3 investigated 40 subjects from Experiment 2 who feigned symptoms of traumatic brain injury (TBI) with 80% of malingering subjects producing digit spans in the abnormal range. A digit span malingering index (DSMI) was developed to detect atypical error patterns in malingering subjects. Overall, 59% of malingering subjects with abnormal digit spans showed DSMIs in the abnormal range and DSMI values correlated significantly with the magnitude of malingering. Experiment 4 compared 29 patients with TBI with a new group of 38 control subjects. The TBI group showed significant reductions in digit span. Overall, 32% of the TBI patients showed DS abnormalities and 11% showed abnormal DSMIs. Computerized error-pattern analysis improves the sensitivity of DS assessment and can assist in the detection of malingering.

Phonological processing in human auditory cortical fields.

We used population-based cortical-surface analysis of functional magnetic imaging data to characterize the processing of consonant-vowel-consonant syllables (CVCs) and spectrally matched amplitude-modulated noise bursts (AMNBs) in human auditory cortex as subjects attended to auditory or visual stimuli in an intermodal selective attention paradigm. Average auditory cortical field (ACF) locations were defined using tonotopic mapping in a previous study. Activations in auditory cortex were defined by two stimulus-preference gradients: (1) Medial belt ACFs preferred AMNBs and lateral belt and parabelt fields preferred CVCs. This preference extended into core ACFs with medial regions of primary auditory cortex (A1) and the rostral field preferring AMNBs and lateral regions preferring CVCs. (2) Anterior ACFs showed smaller activations but more clearly defined stimulus preferences than did posterior ACFs. Stimulus preference gradients were unaffected by auditory attention suggesting that ACF preferences reflect the automatic processing of different spectrotemporal sound features.

Attentional selection in the processing of hierarchical patterns: an ERP study.

The current study aimed to investigate the effect of attentional selection of distinctive local elements on the processing of hierarchically organized patterns. Event-related brain potentials (ERPs) were recorded from subjects during identifications of global or local shapes of hierarchical patterns where either all local elements were identical (homogeneous stimulus) or a local element closest to fixation was distinguished by color from others (pop-out stimulus). One group of subjects was presented with the homogeneous stimuli and required to identify global or local shapes in separate blocks of trials. The other group was presented with the pop-out stimuli and asked to attend to the unique local item in the local task. A global precedence effect was observed in behavioral data. ERPs showed enlarged posterior P1 and N2 amplitudes in the local relative to global conditions. Top-down attention to the pop-out item resulted in increased frontal/central N2 amplitudes in the local condition but eliminated the temporal/occipital N2 enhancement in the local relative to global conditions. Top-down attention to the pop-out item also increased local-to-global interference in reaction times and frontal N2 latencies. The results suggest that a frontal mechanism is involved in directing top-down attention to a specific local item whereas a temporal/occipital mechanism is engaged in an attentional filtering process in the identification of local shapes in hierarchical analysis.

Neural substrates for visual perceptual grouping in humans.

Two experiments investigated the neural mechanisms of Gestalt grouping by recording high-density event-related brain potentials (ERPs) during discrimination tasks. In Experiment 1, stimulus arrays contained luminance-defined local elements that were either evenly spaced or grouped into columns or rows based on either proximity or similarity of shape. Proximity grouping was indexed by a short-latency positivity (110-120 ms) over the medial occipital cortex and a subsequent right occipitoparietal negativity. Grouping by similarity was reflected only in a long-latency occipitotemporal negativity. In Experiment 2, proximity grouping was examined when local elements were defined by motion cues, and was again associated with a medial occipital positivity. However, the subsequent long-latency negativity was now enhanced over the left posterior areas. The implications of these results to the neural substrates subserving different grouping processes are discussed.

Interactions between spatial attention and global/local feature selection: an ERP study.

The present study examined the interaction between spatial attention and global/local feature processing of visual hierarchical stimuli. Event-related brain potentials (ERPs) were recorded from subjects who detected global or local targets at attended locations while ignoring those at unattended locations. Spatial attention produced enhanced occipital P1 and N1 waves in both global and local conditions. Selection of local features enhanced posterior P1, N1 and N2 waves relative to selection of global features. However, the modulations of the P1 and N2 by global/local feature selection were stronger when spatial attention was directed to the left than the right visual fields. The results suggest neurophysiological bases for interactions between spatial attention and hierarchical analysis at multiple stages of visual processing.

The role of spatial frequency in cued shifts of attention between global and local forms.

It has been suggested that shifts of attention between global and local forms might be based on selection between, or differential activation of, low- and high-spatial-frequency channels. In the present study, pretrial cues indicated which level (global or local) was likely to contain the target on each trial. There was a response time (RT) advantage for validly cued trials and an RT cost for invalidly cued trials relative to a neutral cue baseline. This cuing effect was the same for broadband stimuli and for contrast-balanced stimuli in which low spatial frequencies were eliminated. Thus, cued attentional shifts between global and local forms occur even when selection cannot be based on spatial frequency.

Attentional inhibition or paracontrast?

In visual search experiments using asynchronous presentation of target and distractors, a robust and unexpected inhibition of reaction time was observed for the discrimination of a temporally trailing target. A number of experiments were required to determine the source of this inhibition. These experiments eliminated the possibilities that the inhibition might be a manifestation of three attentional processes: inhibition of return, attentional dwell time, or attentional capture by the temporally leading item. Other experiments eliminated the possible preattentional process of the temporal impulse response, the psychological refractory period, and a response inhibition. The characteristics of this inhibition lead to the conclusion that it is a manifestation of paracontrast.

Human brain specialization for phonetic attention.

The effects of auditory selective attention on event related potentials (ERPs) to speech sounds were examined in subjects attending to vowel-consonant-vowels (VCVs) in one ear while ignoring VCVs in the opposite ear. In one condition, subjects discriminated phonetic changes in the VC, CV, or both formant-transition regions. In another condition, they discriminated equally difficult intensity changes in the same VCV regions. Attention-related negative difference waves showed enhanced early and late components (Nde and Ndl) during phoneme-discrimination conditions. Hemispheric asymmetries developed only during the Ndl and were more pronounced during phoneme discrimination. The results suggest that auditory areas of both hemispheres are specialized for phonetic analysis, with hemispherically specialized mechanisms engaged primarily during the final stages of phoneme processing.

Preattentive control of serial auditory processing in dichotic listening.

Dichotic listening performance was examined in an auditory selective attention task where subjects responded to occasional consonant-vowel (CV) or shaped broadband noise-burst (NB) targets in rapid serial auditory presentation (RASP). Trial types were randomized and included monaural CVs and NBs as well as dichotic CV-CV and CV-NB pairings. CVs were spoken by two different voices (male and female), and the two NB stimuli differed in their filter slopes at higher frequencies. The target was designated by stimulus category (/ba/, /da/, /ga/, or NB) and voice (e.g., "female /ba/"). Performance was compared for targets in the left and right ears on monaural and dichotic trials using accuracy and reaction time (RT) measures. Right ear advantages (REAs) were present for CV targets with either CV or NB distractors, but not for monaural CVs. The REA found for monaural NB targets was eliminated by CV distractors, yielding a left ear advantage (LEA) for the distractor effect of CVs on NB targets. The pattern of results suggests initial preprocessing of speech stimuli through phonetic feature analysis, followed by serial attentional processing of the objects in the auditory field. REAs are attributed to a rightward asymmetry in the preattentive control of auditory attention similar to that found in visual search.

Is attentional selection to different levels of hierarchical structure based on spatial frequency?

Target identification is faster when the target level (global or local) is the same as that on the previous trial, presumably because attention is directed to the appropriate level. L. C. Robertson (1996) found that eliminating low spatial frequencies by contrast balancing eliminated this level repetition effect and concluded that attentional selection between different levels of structure is based on spatial frequency. In contrast, M. R. Lamb and E. W. Yund (1996a) found no effect of contrast balancing on the level repetition effect and thus concluded that attentional selection is not based on spatial frequency. In this study, the authors identified the procedural difference between the 2 studies responsible for this difference in results and replicated both findings. The data show that spatial frequency is not a necessary basis for attentional selection between global and local forms. Although it remains possible that spatial frequency is the basis of attentional selection under some circumstances, the data supporting this proposition are not yet compelling.

Phonemes, intensity and attention: differential effects on the mismatch negativity (MMN).

Auditory event-related potentials (ERPs) to speech sounds were recorded in a demanding selective attention task to measure how the mismatch negativity (MMN) was affected by attention, deviant feature, and task relevance, i.e., whether the feature was target or nontarget type. With vowel-consonant-vowel (VCV) disyllables randomly presented to the right and left ears, subjects attended to the VCVs in one ear. In different conditions, the subjects responded to either intensity or phoneme deviance in the consonant. The position of the deviance within the VCV also varied, being in the first (VC), second (CV), or both (VC and CV) formant-transition regions. The MMN amplitudes were larger for deviants in the attended ear. Task relevance affected the MMNs to intensity and phoneme deviants differently. Target-type intensity deviants yielded larger MMNs than nontarget types. For phoneme deviants there was no main effect of task relevance, but there was a critical interaction with deviance position. The both position gave the largest MMN amplitudes for target-type phoneme deviants, as it did for target- and nontarget-type intensity deviants. The MMN for nontarget-type phoneme deviants, however, showed an inverse pattern such that the MMN for the both position had the smallest amplitude despite its greater spectro-temporal deviance and its greater detectability when it was the target. These data indicate that the MMN reflects differences in phonetic structure as well as differences in acoustic spectral-energy structure of the deviant stimuli. Furthermore, the task relevance effects demonstrate that top-down controls not only affect the amplitude of the MMN, but can reverse the pattern of MMN amplitudes among different stimuli.

Spatial nonuniformities in visual search.

Previous search experiments in this laboratory have been concerned with the marked differences in target detectability as a function of its location in the visual field-differences we have called a detectability gradient-when subjects were required to detect a vertically oriented "target" among a number of distractor items having different orientations. This gradient was characterized by a marked right visual field superiority as well as differences in the shape of the gradient in the two half fields. A scanning model was proposed to account for these robust phenomena. The present experiments, using reaction time methods with vertical, horizontal, and colored targets have revealed marked differences in both reaction time and detectability as a function of target location and have isolated some of the spatial nonuniformities in the visual system which influence the shape of these gradients. The results reported here have forced us to abandon the scanning hypothesis in favor of a model in which attention is efficiently guided to the target.

Guided search: the effects of learning.

The previous report (Efron & Yund, 1996) offered an interpretation of the results of a number of search experiments within the theoretical context of the guided search model of Cave and Wolfe (1990) and Wolfe (1994). The present report extends this interpretation to the effects of extended practice when subjects search for a target defined by its orientation in the presence of a number of heterogeneous distractor items having differing orientations. Three experiments are described: The first revealed that over the course of 21 experimental sessions extending for a period of 6 weeks there were marked decreases in the magnitude of the reaction time gradient (RTG) and the right visual field superiority observed in the previous experiments. This learning persisted for more than 3 years. The second experiment revealed an interference in the capacity to learn to detect a target of one orientation when subjects had previously learned to detect a target of a different orientation at the same locations. The third experiment revealed that the learning was restricted to the area of the visual field where the target had been presented and that subjects could learn to detect two different targets concurrently. The results of these experiments indicate that the learning is orientation-specific and location-specific and is consistent with a localized increase in the selectivity of the top-down selection mechanism of the guided search model.

Spatial frequency and attention: effects of level-, target-, and location-repetition on the processing of global and local forms.

Is attentional selection between local and global forms based on spatial frequency? This question was examined by having subjects identify local or global forms of stimuli that had been "contrast balanced," a technique that eliminates low spatial frequencies. Response times (RTs) to global (but not local) forms were slowed for contrast-balanced stimuli, suggesting that low spatial frequencies mediate the global RT advantage typically reported. In contrast, the beneficial effect of having targets appear at the same, as opposed to a different, level as that on the immediately preceding trial was unaffected by contrast balancing. This suggests that attentional selection between different levels of structure is not based on spatial frequency. The data favor an explanation in terms of "priming," rather than in terms of adjustments in the diameter of an attentional "spotlight."

The effect of multichannel compression on vowel and stop-consonant discrimination in normal-hearing and hearing-impaired subjects.

OBJECTIVE: Multichannel compression (MCC) processing can alter the speech spectrum, perhaps reducing spectral contrasts that are important for the discrimination of certain speech sounds. The effect of MCC processing on the discrimination of vowels and voiced stop consonants was studied. DESIGN: Vowels and voiced stop consonants were MCC-processed in two ways: 1) FLAT MCC having the same compression ratio in each channel, and 2)SHAPED MCC having compression ratios in each channel adjusted to the auditory area of the particular subject. The stimuli were processed both ways using 2, 4, 8, 16, and 31 independent compression channels. Unprocessed and linearly amplified stimuli were used as control conditions. Normal-hearing and hearing-impaired subjects were tested for changes in discrimination performance as a function of the MCC processing parameters. RESULTS: When the MCC processing was adjusted specifically for an individual hearing impared subject, no negative effect of increasing numbers of channels (2 to 31)was found. In the case of FLAT MCC processing, increasingly degraded discrimination performance was found for both subject groups as the compression ratio increased and as the number of channels increased. There was also a strong interaction between the effects of the number of channels and the compression ratio, with the negative effects of increasing numbers of channels being much greater at the highest compression ratio. CONCLUSIONS: Negative effects of MCC were found only for very extreme MCC conditions. MCC processing with compression ratios adjusted in each channel for the individual subject, and having as many as 31 channels, revealed no negative effects on vowel or voiced stop-consonant discrimination. These results do not support the prevalent view that MCC with more than two or three channels will be detrimental and should encourage further research on MCC processing with larger numbers of channels.

Discrimination of multichannel-compressed speech in noise: long-term learning in hearing-impaired subjects.

OBJECTIVE: It takes time for an individual to obtain optimal benefit from a new hearing aid. This research examines the possibility that similar long-term learning can be seen in consecutive laboratory studies of multichannel compression (MCC). DESIGN: Three studies of different parameters of MCC processing, carried out over the period of 1 yr, included the same 15 hearing-impaired subjects and one identical MCC-processing condition. The full-range MCC had 8, 12, or 16 independent frequency channels, using a Robinson-Huntington compression algorithm. The City University of New York nonsense syllable test was modified to facilitate digital signal processing and control of the experiments. The subjects discriminated nonsense syllables (a female and a male voice) in speech spectrum noise at -5 to 15 dB signal-to-noise ratios (S/N). Conditions were not ideal for learning: subjects' experience with MCC-processed speech was limited to the laboratory and no trial-by-trial feedback was provided. Percent correct syllable discrimination and consonant confusion matrices were compared across experiments to observe the subjects' learning to listen with MCC processing. RESULTS: All subjects combined, and 14 of 15 individual subjects, showed significant improvement across experiments. For the subject showing the maximum learning, the percent correct difference between the first and third experiments was equivalent to a 9.8 dB increase in S/N. The average learning for all subjects was equivalent to +3 dB S/N. The difference between the consonant-confusion matrices for the first and third experiments indicated that improved discrimination occurred for both manner and place information. The pattern of changes in the confusion matrices was consistent with improved use of the high-frequency information supplied by the MCC signal processing. A brief comparison of the results of the first experiment with a fourth experiment indicated that the learning was specific to MCC processing because it did not generalize to frequency-shaped linear amplification which was also studied in those two experiments. CONCLUSIONS: These results indicate that specific long-term learning occurred for hearing-impaired subjects listening to nonsense syllables in noise with 8- to 16-channel MCC processing. Since previous experiments have provided subjects with much less listening experience, the results suggest that MCC with large numbers of channels may be much more beneficial for the hearing-impaired individuals than the results of previous experiments had indicated.