Decreased axial diffusivity within language connections: a possible biomarker of schizophrenia risk.

Siblings of patients diagnosed with schizophrenia are at elevated risk for developing this disorder. The nature of such risk associated with brain abnormalities, and whether such abnormalities are similar to those observed in schizophrenia, remain unclear. Deficits in language processing are frequently reported in increased risk populations. Interestingly, white matter pathology involving fronto-temporal language pathways, including arcuate fasciculus (AF), uncinate fasciculus (UF), and inferior occipitofrontal fasciculus (IOFF), are frequently reported in schizophrenia. In this study, high spatial and directional resolution diffusion MRI data was obtained on a 3T magnet from 33 subjects with increased familial risk for developing schizophrenia, and 28 control subjects. Diffusion tractography was performed to measure white matter integrity within AF, UF, and IOFF. To understand these abnormalities, Fractional Anisotropy (FA, a measure of tract integrity) and Trace (a measure of overall diffusion), were combined with more specific measures of axial diffusivity (AX, a putative measure of axonal integrity) and radial diffusivity (RD, a putative measure of myelin integrity). Results revealed a significant decrease in Trace within IOFF, and a significant decrease in AX in all tracts. FA and RD anomalies, frequently reported in schizophrenia, were not observed. Moreover, AX group effect was modulated by age, with increased risk subjects demonstrating a deviation from normal maturation trajectory. Findings suggest that familial risk for schizophrenia may be associated with abnormalities in axonal rather than myelin integrity, and possibly associated with disruptions in normal brain maturation. AX should be considered a possible biomarker of risk for developing schizophrenia.

Novel popout with nonsense strings: effects of predictability of string length and spatial location.

Recent studies have shown that when one of four expected words is replaced by a single unexpected word, the unexpected word may capture attention. In three experiments, we explored the generality of this effect. In each experiment, observers viewed arrays composed of four computer-generated "nonsense" strings. Accuracy of string localization was assessed after each array. Some strings, called familiar, appeared in many arrays, whereas others, called novel, appeared in only one. In each experiment, novel strings in arrays composed of one novel and three familiar strings were localized more accurately than were novel strings in arrays composed entirely of novel strings, and familiar strings in these arrays were localized less accurately than were familiar strings in arrays composed entirely of familiar strings. These two effects, termed novel popout and familiar sink-in, respectively, were observed even when novel and familiar strings were rendered less discriminable by holding their lengths constant (Experiment 2) and when familiar strings always appeared in the same spatial locations (Experiment 3). The data suggest that novel objects can capture attention even when the objects lack any clear linguistic referent, when they are superficially similar to the familiar objects that surround them, and when the spatial locations of familiar objects are completely predictable.

Perceptual inhibition of expected inputs: The key that opens closed minds.

The mind appears to be biased simultaneously toward both expected and unexpected inputs. For example, familiar scenes are usually perceived more readily than novel scenes, indicating the former bias, but a single novel object sometimes pops out from a familiar field, indicating the latter bias. A diverse literature and a computational model converge on the following resolution to this paradox: The former bias is conceptually driven and actually suppresses data-driven processing of expected inputs; in turn, this suppression disinhibits data-driven processing of unexpected inputs, yielding the latter bias. Evidence for suppressed data-driven processing of expected inputs is drawn from studies of perceptual habituation, semantic satiation, memory inhibition, inhibition of return, repetition blindness, primed inhibition, the word-inferiority effect, registration without learning, and both expert- and schema-based inhibitory effects. Evidence for enhanced data-driven processing of unexpected inputs is drawn from studies of the orienting response, mismatch negativity, memory facilitation, both expert- and schema-based facilitatory effects, and perceptual popout. The model, calledmismatch theory, incorporates inhibitory and facilitatory perceptual dynamics and is found to simulate the opposing biases. Implications of mismatch theory for perceptual phenomenology, dynamic systems theory, mental health, and individual differences are also discussed.

Long-term perceptual memory for briefly exposed words as a function of awareness and attention.

Two experiments investigated the possibility that perceptual memory for words is dependent on level of awareness of those words. In Experiment 1, subjects attempted to report briefly exposed words in a study phase and then identify words that faded into view in a test phase. Old words appeared in both the study and test phases, whereas new words appeared only in the test phase. Perceptual memory, indexed as the faster identification of old vs. new words, was observed only for words correctly reported in the study phase. In the study phase of Experiment 2, words were flanked by digits, and the distribution of attention between words and digits was varied. Perceptual memory increased from nil to high levels as more attention was allocated to the words. These findings suggest that long-term perceptual memory is dependent on level of awareness of words in the study phase.

Contribution of perceptual fluency to recognition judgments.

Following a shallow (count vowels) or deep (read) study task, old and new words were tested for both fluency of perception and recognition memory. Subjects first identified a test word as it came gradually into view and then judged it as old or new. Old words were identified faster than new words, indicating implicit, perceptual memory for old words. Independently of this effect, words judged old were identified faster than words judged new, especially after shallow study. Eight experiments examined the possible causal relationship between perceptual fluency and recognition judgements. Experiments 1 to 4 showed that fast identifications per se do not promote old judgments. Accelerating the identification of test items by semantically priming them or making them come more quickly into view did not affect recognition judgments. Experiment 5 showed that the usual association of fast identifications with old judgments is not an artifact of item selection because the association disappeared when the identifications and judgements were segregated into different phases of the test task. Experiments 6 and 7 showed tha the likelihood of old judgments increases directly with the pretested perceptibility of test words, but only after shallow study. Experiment 8 showed that the dependency of recognition judgments on perceptual fluency continues to hold when the requirement to identify the words before judging them is eliminated. We conclude that fluency of perception contributes to recognition judgments, but only when the fluency is produced naturally (e.g., through perceptual memory) and explicit memory is minimal.

Attention capture by novel stimuli.

In several experiments, observers were given glimpses of 4-word arrays. Accuracy of word localization was tested after each array. Some words, called familiar, appeared many times across the series of arrays; others, called novel, appeared only once. The ratio of novel to familiar words in an array ranged from 0:4 to 4:0. When familiar and novel words were not intermixed (in 0:4 and 4:0 arrays), localization accuracy was higher for familiar words. However, when they were intermixed, especially in 1:3 arrays, accuracy tended to be higher for the novel words. This novel popout effect was the outcome of the suppressed localizability of the familiar words (relative to the 0:4 baseline) and the enhanced localizability of the novel words (relative to the 4:0 baseline). Novel popout may reflect an automatic orientation of attention away from more fluently unfolding regions of the perceptual field (familiar objects) and toward less fluently unfolding regions (novel objects).