Effects of similarity, difficulty, and nontarget presentation on the time course of visual attention

Long-lasting interference from an initial visual target on a subsequent one has been measured in two paradigms: rapid serial presentation of targets and nontargets at a single location, and simple presentation of two spatially separated targets. We note that comparisons between these paradigms might be invalid, since interference in each paradigm can be attributed to a different source: demands on selective attention, or demands to switch locations. We use a novel target presentation that both minimizes selection demands and eliminates location switching, yet we still find long-lasting interference. We suggest that all three paradigms discussed tap a common attentional limit. We also examine effects of similarity between targets, and effects of discrimination difficulty on the initial target. We find that similarity effects are more pronounced when nontargets are present, and we find no effect of discrimination difficulty on subsequent interference.     

The attentional blink

When two masked targets (T1 and T2) are presented within approximately 500 ms of each other, subjects are often unable to report the second of the two targets (T2) accurately, even though the first has been reported correctly. In contrast, subjects can report T2 accurately when instructed to ignore T1, or when T1 and T2 are separated by more than 500 ms. The above pattern of results has been labelled the attentional blink (AB). Experiments have revealed that the AB is not the result of perceptual, memory or response output limitations. In general, the various theories advanced to account for the AB, although they differ in the specific mechanisms purported to be responsible, assume that allocating attention to T1 leaves less attention for T2, rendering T2 vulnerable to decay or substitution. The present report attempts to bring together these various accounts by proposing a unifying theory. This report also highlights recent attempts to determine if the AB exists across stimulus modalities and points to applications of AB methods in understanding deficits of visual neglect. We conclude by suggesting that investigations of the AB argue in favour of the view that attention may be thought of as a necessary (but not sufficient) condition for enabling consciousness.     

Body Composition And Human Sleep

It has been reported that fit atheletes have more slow wave sleep (SWS), sleep longer and have shorter sleep onset latencies than unfit individuals. However, we have shown that these differences are not a direct consequence of physical fitness. This suggests that the effect is due to more enduring characteristics of individuals. We report two experiments designed to test the hypothesis that individual differences in sleep are related to differences in body composition. The hypothesis was tested in two different experiments, each comparing independent groups of fit athletes with unfit non-athletes. In each experiment both sleep and a number of anthropometric variables were measured. Twenty-five fit and 22 unfit subjects were run in Experiment 1 and 17 fit and 17 unfit in Experiment 2. In Experiment 1 percentage fat was estimated from a skin fold method, while in Experiment 2 lean body mass (LBM) was estimated from 24 h. urinary creatinine. The results showed that percentage LBM was negatively related to SWS in fit subjects, while the amount of LBM and weight were negatively related in the unfit groups. When all subjects were combined within each experiment, significant negative correlations were found between SWS and both LBM and percentage LBM in Experiment 2. The results suggest that body composition influences SWS levels, but not other components of sleep.     

SELF-MONITORING AND WORK PRODUCTIVITY WITH MENTALLY RETARDED ADULTS

We examined the use of self-monitoring to increase the productivity of five mentally retarded adults in a sheltered workshop. Data were collected daily during a 30-minute intervention and 30-minute generalization period. Following baseline, verbal praise, prompts, and physical encouragement were administered contingent on productive behavior on a specific task during the intervention period. In the next phase, self-monitoring was trained during the intervention period. During both phases, baseline conditions prevailed in the generalization periods. In the final phase, self-monitoring was extended across the intervention and generalization periods. Results showed that increased productivity levels, evident when praise and prompting were being administered, maintained with self-monitoring alone. Minimal generalization across time was observed until self-monitoring was begun in the generalization period.     

Processing complexity and sentence memory: evidence from amnesia.

This study examines sentence memory as a function of linguistic processing complexity in amnesic patients. Sentence length as well as lexical and syntactic complexity were manipulated in two sentence repetition experiments. It was found that the amnesic patients performed considerably worse than the control subjects and that performance decreased: (1) when sentence length was increased by the addition of adjuncts compared to arguments of the verb; (2) when the verb selected more thematic frames; and (3) when sentences involved "empty" argument positions that must be linked to antecedents, particularly across clausal boundaries. These data showed how linguistic complexity affects sentence memory and implied that the amnesic deficit did not involve a generalized difficulty for materials of similar length, rather, the deficit was specific to certain representational types and processing routines.     

Rank-reducibility of a symmetric matrix and sampling theory of minimum trace factor analysis

One of the intriguing questions of factor analysis is the extent to which one can reduce the rank of a symmetric matrix by only changing its diagonal entries. We show in this paper that the set of matrices, which can be reduced to rankr, has positive (Lebesgue) measure if and only ifr is greater or equal to the Ledermann bound. In other words the Ledermann bound is shown to bealmost surely the greatest lower bound to a reduced rank of the sample covariance matrix. Afterwards an asymptotic sampling theory of so-called minimum trace factor analysis (MTFA) is proposed. The theory is based on continuous and differential properties of functions involved in the MTFA. Convex analysis techniques are utilized to obtain conditions for differentiability of these functions.     

A large-scale expandable I/O port interface for the TRS-80 microcomputer

Described is a large-scale expandable input/output port interface for the Tandy Corporation TRS-80 microcomputer.