Allocation of visual attention to spatial locations: tradeoff functions for event-related brain potentials and detection performance

Event-related brain potentials (ERPs) were recorded in response to unilateral arrays of letters flashed in rapid, randomized sequences to left and right visual field locations. Subjects were required to focus attention exclusively on either left or right field stimuli, or to divide attention in different proportions between the two fields, with the aim of detecting infrequent target letters. Both d' and percent hits for target detections increased significantly as attentional allocation to a stimulus location increased. Attention operating characteristic (AOC) curves for the target detection scores were highly similar in form to those for the amplitudes of the long-latency, endogenous ERP components--N350-650 and P400-800 (P300). All of these measures showed gradual, nearly rectangular tradeoff functions. In contrast, the AOC curves for the early sensory-evoked components displayed steep, nearly linear amplitude tradeoffs as attention was increasingly allocated to one visual field at the expense of the other. The early and late ERP components were considered as indices of separate but interacting levels of attentional selection having different operating principles.     

The dynamics of learning and allocation of study time to a region of proximal learning

In contrast to the dominant discrepancy reduction model, which favors the most difficult items, people, given free choice, devoted most time to medium-difficulty items and studied the easiest items first. When study time was experimentally manipulated, best performance resulted when most time was given to the medium-difficulty items. Empirically determined information uptake functions revealed steep initial learning for easy items with little subsequent increase. For medium-difficulty items, initial gains were smaller but more sustained, suggesting that the strategy people had used, when given free choice, was largely appropriate. On the basis of the information uptake functions, a negative spacing effect was predicted and observed in the final experiment. Overall, the results favored the region of proximal learning framework.     

Partial integration of single electrocutaneous pulses

Psychometric functions generated by single eleetroeutaneous stimuli yielded a median coefficient of variation ( σ/μ ) of 0.23. These data are consistent with other psychometric data recently reported by us which yielded σ/μ ratios of this size. The data are discussed and related to conflicting data reported in the recent literature indicating coefficients of variation for this mode of stimulation which are only 1/3 as large. Evidence is presented for partial temporal summation (time-intensity reciprocity) for electrocutaneous stimuli ranging from 175 to 610 microseconds. The data are best fitted by the equation I x t^a = k, where a is approximately 0.57. This equation and exponent also fit summation data reported by the same authors who report finding steep psychometric functions. Clearly, then, the mechanism responsible for the very limited temporal summation found for eleetrocutaneous stimulation and the mechanism responsible for very steep psychometric functions are not identical. The discussion also includes speculation regarding possible mechanisms and suggestions for research.     

Analysis of simple reaction time to a sinusoidal grating by means of a linear filter model of the detection process

Simple reaction time (RT) to a sinusoidal grating was analyzed in terms of a linear filter model of the detection process. First, RT contrast functions were determined over a wide range of spatial frequencies and retinal illuminances. Second, calculating the time course of the linear filter's response, theoretical visual latency contrast functions were derived for the same conditions of spatial frequency and retinal illuminance as those in the RT measurements. Comparison of the two functions showed that the contrast dependence of the RT functions was much larger than that of the visual latency functions. The discrepancy between the two functions was satisfactorily described as a power function of the slope of the filter's response at threshold level. On the basis of these results, we propose a model of the RT process. According to the model, the RT process is mediated by a cascade that consists of a level detector, which includes a linear filter followed by a threshold device, and a differentiator of the filter's response.     

The Stiles-Crawford effect of the first kind (SCE I): studies of SCE I in an aniridic observer

The Stiles-Crawford effect of the first kind (SCE I), discovered in 1933, represented a major breakthrough in our understanding of retinal physiology and the modern beginning of the science of photoreceptor optics. The current status of knowledge in this area is briefly reviewed. A study is presented of a white adult female observer with aniridia, clear media, only traces of nystagmus, rather good visual acuity, and good fixation. It is shown that this individual exhibits approximate alignment of her photoreceptors with the center of the retinal sphere, clear evidence of side lobes on functions, and surprisingly steep SCE I functions. The implications of these findings are considered.     

On the general form of Stevens’ law for loudness and softness

The loudness of a 1000-Hz tone at weak sound pressures and its softness at intense ones were scaled by the method of magnitude estimation. Estimates of loudness plotted as a function of sound pressure on double logarithmic coordinates showed the well-documented steepening near threshold. A similar steepening occurred in the softness function at high intensities. Stevens’ law, which is linear on these coordinates, could be recovered either by translating the pressure scale to a new origin, or by translating the response scale. Translations of the response scale were preferred because they produced functions in which loudness and softness were reciprocally related, whereas transformations of the stimulus made the softness function almost three times as steep as the loudness function.     

Judgments of learning: Evidence for a two-stage process

Three experiments tested the hypothesis that people make judgments of learning (JOLs) by attempting to retrieve the target first. If this were the whole story, then the reaction time (RT) functions for making JOLs with no special instructions would parallel those found when people are told to first attempt retrieval and then make a JOL. In the present data, monotonic functions, showing an increase in RT with decreasing JOL, were found when people were instructed to retrieve covertly or overtly and then make a JOL, as would be expected if retrieval fluency entirely determined JOLs. However, the functions for making uninstructed JOLs were different: Low JOLs were made quickly, not slowly, and the curves were inverted U shapes, rather than linear. Furthermore, people's memory performance was somewhat better, especially on low-JOL items, when they were instructed to first retrieve as opposed to when they were told only to make JOLs. To account for these data, we propose a two-stage model of JOLs, with the first stage occurring prior to attempted retrieval.     

Tactile stimulation: Psychophysical studies of receptor function

Psychometric functions for the detection of brief tactile pulses were determined at the fingertips and the dorsal forearm. Functions at both lore were shallower than those previously obtained for electrocutaneous pulses. demonstrating the different neural consequences of receptor and afferent nerve stimulation. Detection on the forearm was characterized by steeper slopes of psychometric functions and by lower rates of false alarms than on the fingertips, though absolute sensitivity was better at the latter site. An examination is made of explanations for the differential effects based on receptor type, receptor density, and static tremor.     

Local supersaturation during melting in a temperature gradient

A homogeneous single-phase Al–Cu alloy was exposed to a steep temperature gradient for a short time interval, melting of the sample at the hot end was interrupted at intermediate stages. In the resolidified microstructure, the local supersaturation was determined by analysing concentration profiles across former liquid films at grain boundaries and adjacent zones in the grain interior. Already at moderate heating rates (3 K/s) significant supersaturations occurred and were quantified.     

Eye movements serialize memory for objects in scenes

A gaze-contingent short-term memory paradigm was used to obtain forgetting functions for realistic objects in scenes. Experiment 1 had observers freely view nine-item scenes. After observers' gaze left a predetermined target, they could fixate from 1-7 intervening nontargets before the scene was replaced by a spatial probe at the target location. The task was then to select the target from four alternatives. A steep recency benefit was found over the 1-2 intervening object range that declined into an above-chance prerecency asymptote over the remainder of the forgetting function. In Experiment 2, we used sequential presentation and variable delays to explore the contributions of decay and extrafoveal processes to these behaviors. We conclude that memory for objects in scenes, when serialized by fixation sequence, shows recency and prerecency effects that are similar to isolated objects presented sequentially over time. We discuss these patterns in the context of the serial order memory literature and object file theory.     

Determination of a behavioral transfer function: White-noise analysis of session-to-session response-ratio dynamics on concurrent VI VI schedules

Six pigeons were exposed to concurrent variable-interval schedules in which the programmed reinforcer ratios changed from session to session according to a pseudorandom binary sequence. This procedure corresponded to the stochastic identification paradigm (“white-noise experiment”) of systems theory and enabled the relation between log response ratios in the current session and log reinforcer ratios in all previous sessions to be determined. Such dynamic relations are called linear transfer functions. Both nonparametric and parametric representations of these, in the form of “impulse-response functions,” were determined for each bird. The session-to-session response ratios resulting from the session-to-session pseudorandom binary variations in reinforcer ratios were well predicted by the impulse-response functions identified for each pigeon. The impulse-response functions were well fitted by a second-order dynamic model involving only two parameters: a time constant and a gain. The mean time constant was 0.67 sessions, implying that the effects of abrupt changes in log reinforcer ratios should be 96% complete within about five sessions. The mean gain was 0.53, which was surprisingly low inasmuch as it should equal the sensitivity to reinforcement ratio observed under steady-state conditions. The same six pigeons were subjected to a similar experiment 10 months following the first. Despite individual differences in impulse-response functions between birds within each experiment, the impulse-response functions determined from the two experiments were essentially the same.     

Temporal summation of 500-Hz tones and octave-band noise bursts in infants and adults

A visually reinforced operant procedure was employed to obtain 2-point threshold-duration functions in 7-month-old infants and adults in two experimental paradigms. In Experiment 1, thresholds were determined for 10- and 100-msec, 500-Hz tones and octave-band noise bursts presented in quiet and noise backgrounds. Threshold-duration functions were significantly steeper for infants than for adults under all experimental conditions, and did not differ in slope as a result of differences in either stimulus bandwidth or masking noise. In Experiment 2, thresholds for trains of brief 500-Hz tone pulses were examined in infant and adult subjects. Infant functions were adult-like for integration of multiple-pulse stimuli, suggesting that the traditional, long-term process of temporal summation is mature by 7 months of age. Differences between the present results and those previously obtained for 4-kHz stimuli appear to be consistent with the view that different mechanisms are involved in the detection of low- and high-frequency signals.     

The equiratio taste mixture model successfully predicts the sensory response to the sweetness intensity of complex mixtures of sugars and sugar alcohols

The equiratio taste mixture model was originally developed for the prediction of psychophysical power functions of equiratio mixtures of substances that have a similar taste and that also exhibit mutual cross adaptation. Earlier studies have shown that the model is valid for mixtures of sugars and/or sugar alcohols. Two experiments are reported in which it is questioned whether the psychophysical functions of mixtures of higher physical complexity can be predicted by the model. In the first experiment the psychophysical power functions of binary and quaternary equiratio mixture types were determined experimentally and compared to those predicted by the generalized model. In the second, similar, experiment quaternary and eight-component mixture types were examined. The method of magnitude estimation, in combination with the sip and spit procedure, was used. The functions predicted by the model were almost identical to the functions established on the basis of the experimental data. These results reconfirm that the gustatory modality operates like an 'averaging' system when processing this kind of mixture. It is argued that for other kind of mixtures the model will predict incorrectly. The status of the equiratio mixture model is discussed.     

Magnitude scales for cold pressor pain

Subjects in two experiments immersed a hand and forearm in ice water (cold pressor test) for 60 sec and gave magnitude estimates of pain every 5 sec. Forty subjects immersed an arm for three trials in Experiment 1, and 60 subjects immersed an arm for two trials in Experiment 2. Linear, power, or additive constant functions fitted the data almost equally well. Exponents of the two-constant power function differed from those of the additive constant function. Individual differences in exponents were marked, but various psychological manipulations aimed at reducing pain failed to affect the exponents. The utility of power functions to describe cold pressor pain has yet to be determined.     

执行功能可分离性及与年龄关系的潜变量分析

应用潜变量分析研究抑制优势反应、记忆刷新和注意转换三种执行功能的可分离性,以及与年龄的关系。被试为18~85岁的健康成年人142名,完成九项执行功能任务。结果显示：本研究设计的九项执行功能任务有较好的信度;验证性因子分析显示,九项任务与对应执行功能间的因子负荷较高（汇聚性效度好）,而不同执行功能间的相关较低（鉴别性效度好）;在此基础上建立了三种执行功能及其与年龄关系的潜变量分析模型。研究结果表明,执行系统不是单一的认知结构,可以分离为若干相对独立的执行加工过程。     

Binaural summation after learning psychophysical functions for loudness

Do response-related processes affect perceptual processes? Sometimes they may: Algom and Marks (1990) produced different loudness exponents by manipulating stimulus range, and thereby also modified the rules of loudness summation determined by magnitude scaling. The present study manipulated exponents by having a dozen subjects learn prescribed power functions with exponents of 0.3, 0.6, or 1.2 (re sound pressure). Subjects gave magnitude estimates of the loudness of binaural signals during training, and of monaural and binaural signals after training. During training, subjects’ responses followed the nominal functions reasonably well. Immediately following training, subjects applied the numeric response scales uniformly to binaural and monaural signals alike; the implicit monaural-binaural loudness matches, and thus the basic rules underlying binaural summation, were unaffected by the exponent learned. Comparison of these results with those of Algom and Marks leads us to conclude that changing stimulus range likely influences underlying perceptual events, whereas “calibrating” a loudness scale through pretraining leaves the perceptual processes unaffected.     

Psychophysics in the field: Perception and memory for labor pain

Separate groups of women estimated the painfulness of labor contractions either immediately (perceptual judgments) or at time intervals varying from 8 to 48 h after their completion (memorial judgments). The pain judgments of individual uterine contractions were related functionally to the biometrically measured magnitude of these contractions. Perceived and remembered painful sensations were related to referent intensities by power functions governed, as a rule, by exponents greater than unity. Exponents for the memory functions were consistently greater than those for the perceptual functions. Psychophysics done in the field can help decide theoretical issues in addition to providing useful practical information.     

Audio analgesia: Lack of a cross-masking effect on taste

The effects of intense acoustic stimulation on the sense of taste were examined in two experiments. In the first, a yes-no psychophysical method was used to obtain psychometric functions for the discriminability of weak solutions of NaCl or sucrose from distilled water. The functions for NaCl were about 10 times steeper than those for sucrose. In the second experiment, suprathreshold concentrations of these substances were used in conjunction with a magnitude-estimation technique. With neither technique were there any systematic differences in the data taken with and without audio analgesia.     

Developmental fractionation of working memory and response inhibition during childhood

The lateral prefrontal cortex (LPFC) plays a major role in both working memory (WM) and response inhibition (RI), which are fundamental for various cognitive abilities. We explored the relationship between these LPFC functions during childhood development by examining the performance of two groups of children in visuospatial and auditory WM tasks and a go/no-go RI task. In the younger children (59 5- and 6-year-olds), performance on the visuospatial WM task correlated significantly with that in the auditory WM task. Furthermore, accuracy in these tasks correlated significantly with performance on the RI task, particularly in the no-go trials. In contrast, there were no significant correlations among those tasks in older children (92 8- and 9-year-olds). These results suggest that functional neural systems for visuospatial WM, auditory WM, and RI, especially those in the LPFC, become fractionated during childhood, thereby enabling more efficient processing of these critical cognitive functions.     

Linear modeling of steady-state behavioral dynamics

The observed steady-state behavioral dynamics supported by unsignaled periods of reinforcement within repeating 2,000-s trials were modeled with a linear transfer function. These experiments employed improved schedule forms and analytical methods to improve the precision of the measured transfer function, compared to previous work. The refinements include both the use of multiple reinforcement periods that improve spectral coverage and averaging of independently determined transfer functions. A linear analysis was then used to predict behavior observed for three different test schedules. The fidelity of these predictions was determined.