The spatial spread of attentional modulation of the motion aftereffect

The spatial spread of attentional modulation of selective adaptation was investigated in four experiments in which the duration of the movement aftereffect (MAE) was measured with and without processing of intermittently changing digits at the fixation point. In the first experiment, the effects of diverting attention on MAE duration were found to reduce as the distance between the fixation digits and the inner edge of the surrounding adapt/test grating was increased. A second experiment suggested that eye movements were unlikely to underlie the attentional effects. In experiment 3, the attentional effect stayed constant as the outer diameter of the adapt/test gratings was increased. In experiment 4 (as in experiment 1) the modulatory effects of attention were larger the closer the adapt/test gratings were to the locus of attention, when the area of the grating was held constant but its eccentricity varied. In experiments 1 and 4, an intermittently changing fixation digit was found to reduce MAE durations more than an unchanging digit, even when subjects were not required to process it, suggesting that exogenous as well as endogenous attentional processes modulate early motion processing.     

Using both an auditory and a visual short-term store to increase digit span

Can digit span be increased by storing digits nonredundantly in both an auditory short-term store and a visual short-term store (dual storage)? In Experiment 1, when four digits were presented visually and then the remaining digits were presented auditorily, digit span increased three digits over a baseline measurement, but only when the auditorily presented digits were reported first (inverted response). Normal order of response for this presentation was not as effective. Possible reasons for the advantage of inverted response are suggested, based upon dual storage. For all-auditory and all-visual presentations that controlled for parsing, digit span increased only 1 to 1.5 digits over baseline, and inverted and normal order of response did not differ. Experiment 2 demonstrated that an improvement for dual storage could occur when the type of presentation was held constant and the order of response was normal rather than inverted. The results are consistent with the idea of separate auditory and visual short-term stores.     

Beoadbent's filter theory: Postulate H and the problem of switching time

Groups of digits were presented binaurally and dichotically to subjects who were asked to recall them. Different rates and patterns of presentation were used, the design being based on that of Broadbent (1954). Broadbent's findings in this field were confirmed. If subjects are presented with simultaneous pairs of digits at a rate of 2 pairs per second dichotically, they cannot recall them if they are asked to alternate between the ears. If however the presentation is staggered, so that although the rate is constant the signals do not overlap, subjects can recall alternately from the two ears. It is suggested that these findings are better interpreted as an interference effect, not a rate effect. Criticism is offered of similar designs to measure “switching rate”. Criticism is also offered of Broadbent's estimate of “perception time” in such experiments. An analysis of the quantity and type of errors made by subjects is given, which suggests that Broad-bent's theory of a short term store on the peripheral side of a selective filter is in need of revision.     

Buffer storage modality and identification time in tachistoscopic recognition

According to Sperling's (1967) model of short-term memory briefly presented masked stimuli are rapidly read into a non-visual Recognition Buffer (the RB model). An alternative interpretation of the data is that the stimulus information is coded into a non-iconic Visual Buffer where it is held while a much slower recognition process takes place (the VB model). The high frequency of errors in experiments with sequentially presented stimuli appears to refute the possibility that recognition is as rapid as suggested by the RB model. However these data may be attributed to variations in effective stimulus duration and stimulus quality rather than to slow recognition time. In an experiment to control for these effects, normal, laterally inverted and spaced digits were presented in a rapid sequence (1-10 items/s) with intervening pattern masks to keep the stimulus/mask interval constant. The recall data showed that order errors increased with rate of presentation but that item errors remained invariant. At the fastest rates of presentation there were fewer order errors for spaced than for coincident digits. It was argued that the results, as a whole, were more consistent with the VB than the RB model and that there is no evidence for identification times as fast as 10-40 ms/item.     

Selection of objects and tasks in working memory

When people hold several objects (such as digits or words) in working memory and select one for processing, switching to a new object takes longer than selecting the same object as that on the preceding processing step. Similarly, selecting a new task incurs task- switching costs. This work investigates the selection of objects and of tasks in working memory using a combination of object-switching and task-switching paradigms. Participants used spatial cues to select one digit held in working memory and colour cues to select one task (addition or subtraction) to apply to it. Across four experiments the mapping between objects and their cues and the mapping between tasks and their cues were varied orthogonally. When mappings varied from trial to trial for both objects and tasks, switch costs for objects and tasks were additive, as predicted by sequential selection or resource sharing. When at least one mapping was constant across trials, allowing learning of long-term associations, switch costs were underadditive, as predicted by partially parallel selection. The number of objects in working memory affected object-switch costs but not task-switch costs, counter to the notion of a general resource of executive attention.     

The dependence of monocular rivalry on spatial frequency: some interaction variables

The effect of spatial frequency upon the rate of monocular rivalry has been investigated on several occasions, with conflicting results. With increases in spatial frequency the rivalry rate has been variously reported as declining monotonically, increasing slightly and briefly before declining sharply, or showing a sharp increase before a sharp decrease. Experiments are reported which show that all three functions may be obtained depending on whether the number of cycles of the gratings is held constant across spatial frequency, or the field size is held constant (and, if the latter, what field size is used). The point at which any high-frequency decline occurs is also shown to increase with increasing luminance. All functions obtained correspond to visual sensitivity functions obtained under comparable conditions.     

Studies in Vision: IV. The Interactions of Rods and Cones in After-Sensations

Fixed-ratio (FR) size was increased for pigeons (N = 6), while the number of eating responses at reinforcement was either held constant or increased. Also, FR size was held constant while the number of eating responses at reinforcement was increased. Major findings were as follows: (a) when eating responses were held constant, higher FR requirements led to stable key rates and postreinforcement pauses; (b) allowing more eating responses at successively higher FR requirements led to stable key rates and postreinforcement pauses; (c) at high FR requirements which produced low key rates, increasing the number of eating responses at reinforcement increased key rates; and (d) eating response rates varied systematically with key rates.     

Numerical representation: abstract or nonabstract?

Until now it has been a commonly held view that numbers are represented abstractly in the human brain. However, a recent imaging study challenged the existence of an abstract representation at least of digits and number words, at the brain level, and argued that previous studies and paradigms were not sensitive enough to detect deviations from abstract representation at the behavioural level. The current study addressed this issue with an analysis of distance and sequential effects in magnitude classification. Previous studies that used this paradigm did not find deviation from abstract representation for digits and number words (e.g., Dehaene, 1996; Schwarz & Ischebeck, 2000). However, in the current study a short stimulus-response interval was used, which reduced subjective expectancy and increased automatic processing. The current results showed deviation from abstract representation in both reaction time and accuracy and therefore support the idea that nonabstract representations of numbers do exist.     

Repeated vs varied distractors in immediate memory

Ss heard groups of eight spoken digits presented for immediate recall. Irrelevant distractor letters were interpolated between digits, using either the same letter interpolated eight times or eight different letters. The latter condition produced significantly more errors in recall. Error scores were also affected by rate of presentation of items and by whether letter-digit sequences started with a letter or a digit. It is suggested that selective immediate recall may bear some resemblance to aspects of visual search.     

Bar press and bar release as avoidance responses

Two experiments were performed in which rats had to avoid shock by both pressing and releasing a bar within specified intervals. When the release-shock interval was held constant and the press-shock interval was increased, response rate decreased and bar holding increased. When the press-shock interval was held constant and the release-shock interval was increased, both response rate and bar holding decreased.     

Allocation of study time and recall by learning disabled and nondisabled children of different ages

Study time and recall by learning-disabled and nondisabled children of five different ages were examined in a task requiring recall of digits that were presented at the child's own rate. Recall increased with age and was significantly higher by nondisabled than disabled children, particularly at older ages. As additional digits of each sequence were presented, study time by 8-year-old disabled and nondisabled groups were relatively constant, increased in older disabled and nondisabled children, but increased more in older nondisabled children than older learning disabled children. Instructions in hierarchical grouping of digits increased recall by all groups to a similar degree, but the increase by younger children and learning disabled children was associated with longer study times. The results suggest that allocation of study time and recall are developmentally delayed in learning disabled children.     

The role of second formant transitions in the stop-semivowel distinction

An experiment was conducted which assessed the relative contributions of three acoustic cues to the distinction between stop consonant and semivowel in syllable initial position. Subjects identified three series of syllables which varied perceptually from [ba] to [wa]. The stimuli differed only in the extent, duration, and rate of the second formant transition. In each series, one of the variables remained constant while the other two changed. Obtained identification ratings were plotted as a function of each variable. The results indicated that second formant transition duration and extent contribute significantly to perception. Short second formant transition extents and durations signal stops, while long second formant transition extents and durations signal semivowels. It was found that second formant transition rate did not contribute significantly to this distinction. Any particular rate could signal either a stop or semivowel. These results are interpreted as arguing against models that incorporate transition rate as a cue to phonetic distinctions. In addition, these results are related to a previous selective adaptation experiment. It is shown that the “phonetic” interpretation of the obtained adaptation results was not justified.     

Attentionally splitting the mass distribution of hand-held rods

Two experiments on the length-perception capabilities of effortful or dynamic touch differed only in terms of what the subject intended to perceive, while experimental conditions and apparatus were held constant. In each trial, a visually occluded rod was held as still as possible by the subject at an intermediate position. For two thirds of the trials, a weight was attached to the rod above or below the hand. In Experiment 1, in which the subject's task was to perceive the distance reachable with the portion of the rod forward of the hand, perceived extent was a function of the first moment of the mass distribution associated with the forward portion of the rod, and indifferent to the first moment of the entire rod. In Experiment 2, in which the task was to perceive the distance reachable with the entire rod if it was held at an end, the pattern of results was reversed. These results indicate the capability of selective sensitivity to different aspects of a hand-held object's mass distribution, without the possibility of differential exploration specific to these two tasks. Results are discussed in relation to possible roles of differential information, intention, and self-organization in the explanations of selective perceptual abilities.     

Nonverbal representation of time and number in adults

A wealth of human and animal research supports common neural processing of numerical and temporal information. Here we test whether adult humans spontaneously encode number and time in a paradigm similar to those previously used to test the mode-control model in animals. Subjects were trained to classify visual stimuli that varied in both number and duration as few/short or many/long. Subsequently subjects were tested with novel stimuli that varied time and held number constant (eight flashes in 0.8-3.2s) or varied number and held time constant (4-16 flashes in 1.6s). Adult humans classified novel stimuli as many/long as monotonic functions of both number and duration, consistent with simultaneous, nonverbal, analog encoding. Numerical sensitivity, however, was finer than temporal sensitivity, suggesting differential salience of time and number. These results support the notion that adults simultaneously represent the number and duration of stimuli but suggest a possible asymmetry in their representations.     

Escape behavior under different fixed ratios and shock intensities

The effects of ratio length and shock intensity on bar pressing were examined in three rats in two escape-from-shock experiments. In Experiment I, shock intensity was held constant while the schedule was varied from FR 1 to FR 20. The latency of the first escape response increased with FR length while the escape rate, computed as over-all rate in shock minus latency of the first response, decreased at FR 20. In Experiment II, the schedule was held constant at FR 5 while shock intensity was manipulated. Latency decreased as intensity increased, while escape rate increased with intensity, passing through a maximum for two subjects. Responses occurring during the last 100 sec of the 2-min escape period decreased as the FR increased for all subjects, and decreased as shock intensity increased for two subjects.     

Human Signal-detection Performance: Effects Of Signal Presentation Probabilities And Reinforcer Distributions

University students participated in one of four standard two-choice signal-detection experiments in which signal presentation probability was varied and the reinforcement distribution was held constant and equal. In Experiments 1, 3 and 4, subjects' performance showed a systematic response bias for reporting the stimulus presented least often. Experiments 1 and 4 showed that this effect was reliable with extended training and monetary, rather than point, reinforcement. In Experiment 2, all correct responses were signaled in some way, and this produced the opposite relationship between signal presentation probability and response bias. Experiments 1 and 3 found that explicitly deducting money (intended as punishment) for equal numbers of incorrect responses on each alternative, or varying the obtained overall rate of reinforcement, produced no clear change in response bias. The bias, shown by humans, for reporting the stimulus presented least often remains a challenge for theories of stimulus detection.     

Visual selection from multielement displays: measuring and modeling effects of exposure duration

In a partial-report experiment, subjects reported the digits from a circular array of digits and letters terminated by a pattern mask. Individual frequency distributions of the number of correctly reported digits were analyzed as functions of number of digits (2, 4, or 6) and number of letters (0, 2, 4, 6, or 8) at nine exposure durations ranging from 10 to 200 ms. The distributions (hundreds of data points per subject) were accurately predicted by a four-parameter fixed-capacity independent race model that assumes exponentially distributed processing times, limitations in both processing capacity and storage capacity, and time-invariant selectivity. Estimated from the data, processing capacity C was 45 items/s, selectivity alpha (ratio between the amount of processing capacity devoted to a distractor and the amount devoted to a target) was 0.48, short-term storage capacity K was 3.5 items, and the longest ineffective exposure duration t0 was 18 ms.     

The impact of order incongruence between a task-irrelevant auditory sequence and a task-relevant visual sequence

A novel effect is reported in which serial recall of visual digits was disrupted to a greater degree by the presence of the same set of digits presented as an irrelevant auditory sequence than by the presence of irrelevant auditory consonants, but only when the order of the irrelevant digits was incongruent with that of the to-be-remembered digits (Experiment 1). Experiment 2 replicated this order-incongruence effect and showed also that disruption was dictated by the number of order-incongruent transitions but not by the number of novel tokens contained within the irrelevant sequence. The results favor an interference-by- process approach to the disruption of serial memory by irrelevant sound over approaches based on notions of interference by content and/or interference by depletion of attentional resources.     

The influence of selective attention in peripheral and foveal vision

Previous research had indicated that there were differences in the kinds of stimulus information processed by concentrated and distributed attention in peripheral vision. Concentrated attention was necessary for perceiving line arrangement differences, while line slant differences could be detected with distributed attention. However, experiments with foveal presentation showed no facilitation by concentrating attention. Experiment I replicated these results. Experiment II showed that distributed attention did degrade foveal line arrangement discrimination if the attention system was overloaded by increasing the number of elements in the array. Experiment III demonstrated that high element density was not a sufficient condition for these effects to occur. Line arrangement discrimination was reduced as letter number increased even when maximum density was held constant. In Experim~ent IV, it was shown that concentrating attention facilitated line arrangement discrimination relative to line slant discrimination in foveal vision when element number and density were held constant. The results are discussed in terms of several models postulating a difference between spread-out and concentrated attention systems.     

Spatial and temporal task characteristics as stress: a test of the dynamic adaptability theory of stress, workload, and performance

The goal for this study was to test assertions of the dynamic adaptability theory of stress, which proposes two fundamental task dimensions, information rate (temporal properties of a task) and information structure (spatial properties of a task). The theory predicts adaptive stability across stress magnitudes, with progressive and precipitous changes in adaptive response manifesting first as increases in perceived workload and stress and then as performance failure. Information structure was manipulated by varying the number of displays to be monitored (1, 2, 4 or 8 displays). Information rate was manipulated by varying stimulus presentation rate (8, 12, 16, or 20 events/min). A signal detection task was used in which critical signals were pairs of digits that differed by 0 or 1. Performance accuracy declined and workload and stress increased as a function of increased task demand, with a precipitous decline in accuracy at the highest demand levels. However, the form of performance change as well as the pattern of relationships between speed and accuracy and between performance and workload/stress indicates that some aspects of the theory need revision. Implications of the results for the theory and for future research are discussed.