Determinants of infant visual fixation: evidence for a two-process theory

Three experiments were conducted to investigate the dynamics of the human infant's (4 months old) visual fixation. The general finding that, over a series of trials, infants fixate longer to a complex than to a simple stimulus was replicated. The function relating fixation time to trials was shown to be nonmonotonic when the stimulus was complex (fixation time increased between Trials 1 and 2 and then decreased), but was monotonic when the stimulus was simple (it decreased systematically over trials). Additional experiments indicated that (a) the nonmonotonic function associated with the complex stimulus was eliminated when the interval separating Trials 1 and 2 was increased from 10 to 20 or 30 s (Experiment 2), and (b) the difference in fixation time between the complex and the simple stimulus was eliminated by controlling their effects in a within-subjects design (Experiment 3). These data challenge the prevailing cognitive-schema theories as a complete account of the dynamics of the infant's visual fixation. A two-process theory that accounts for these data was proposed.     

Heart-rate and electrodermal orienting responses to visual stimuli differing in complexity

Orienting response (OR) theory predicts that amount of information in the stimulus, or stimulus complexity, should be an important determinant of OR elicitation and habituation, more intense and more slowly habituating ORs being expected to complex than to simple stimuli. This prediction was tested in an experiment where subjects were exposed to simple and complex visual stimuli in randomized order, while heart-rate and skin conductance were measured. Complex stimuli evoked a more pronounced deceleratory heartrate response than did simple stimuli. However, the two conditions did not differ in rate of habituation of this response. For skin conductance responses, on the other hand, the complex stimulus took more trials than the simple stimulus to reach habituation, whereas the two conditions did not differ in response magnitude. Thus, the hypothesis of more intense orienting to complex stimuli was supported by the heart-rate data, and that of slower habituation to complex stimuli, of the skin conductance data.     

Effects of ageing on visual discrimination learning in Drosophila melanogaster

Two experiments examined conditioned suppression of the Proboscis Extension Response (PER), unconditionally released by sucrose stimulation of gustatory tarsal receptors, in young (7-day-old), middle-aged (30-day-old) and old (50-day-old) Drosophila melanogaster males, reared at 25°C. Individual flies were trained in a differential conditioning procedure in which a white stimulus signalled a quinine reinforcer, whereas a black stimulus was non-reinforced. When trained from the outset with the discriminative procedure, flies of all ages acquired the discrimination, although the acquisition of PER suppression to the white stimulus was retarded in middle-aged and old flies. The retardation of the acquisition of PER suppression in middle-aged and old flies was replicated in a second study in which the flies received simple conditioning to the white stimulus prior to discrimination training.     

Scaling extrafoveal detection of distortion in a face and grating

Peripheral performance involving simple visual tasks and stimuli can be equated with foveal performance by spatial scaling, whilst more complex tasks and stimuli seem to need additional scaling of image contrast. We therefore determined whether the contrast manipulation needed to compensate for eccentricity-dependent performance changes is due to an increase in stimulus or task difficulty. We measured contrast sensitivities to determine foveal and peripheral ability to discriminate between an original and a distorted version of a polar-circular sinusoidal grating and a face image. Contrast sensitivities as a function of image size were spatially scaleable across eccentricities for both the face and grating. Furthermore, irrespective of stimulus, performance could be scaled with the same individual E2 value. Thus task simplicity overrides the nature of the stimulus in determining scaling requirements, suggesting that it is the complexity of the task, not of the stimulus, that makes contrast scaling necessary in complex tasks.     

Preparatory Set,Response Complexity,and Reaction Latency

The interaction between preparatory set and response complexity was demonstrated in an experiment investigating the reaction latency of discrete arm movements. Following simple finger-lift reaction-time (RT) trials, subjects performed simple and complex versions of a discrete horizontal arm movement under one of two enforced preparatory set conditions. For the simple task, requiring subjects to attend to the components of the response prior to stimulus presentation (enforced motor set) produced significantly shorter RTs than when concentration was on the stimulus (enforced sensory set). However, RT differences for the complex version of the task failed significance. Theoretical implications of the results for Henry’s (1960) memory drum theory of neuromotor reaction were discussed.     

The development of attention to simple and complex visual stimuli in infants: Behavioral and psychophysiological measures

The study of visual attention in infants has used presentation of single simple stimuli, multi-dimensional stimuli, and complex dynamic video presentations. There are both continuities and discontinuities in the findings on attention and attentiveness to stimulus complexity. A continuity is a pattern of looking that is found in the early part of infancy that remains throughout adulthood. A discontinuity is an emerging sensitivity to the content of the information in the stimulus presentations and alterations in patterns of attention based upon stimulus comprehensibility. The current paper reviews some of these findings with particular application to complex video presentations.     

The effects of concurrent task interference on category learning: evidence for multiple category learning systems

Participants learned simple and complex category structures under typical single-task conditions and when performing a simultaneous numerical Stroop task. In the simple categorization tasks, each set of contrasting categories was separated by a unidimensional explicit rule, whereas the complex tasks required integrating information from three stimulus dimensions and resulted in implicit rules that were difficult to verbalize. The concurrent Stroop task dramatically impaired learning of the simple explicit rules, but did not significantly delay learning of the complex implicit rules. These results support the hypothesis that category learning is mediated by multiple learning systems.     

Stimulus selection in passive avoidance learning and retention: weanling, periadolescent, and young adult rats

Periadolescent rats exhibit a number of behavioral differences in comparison with younger or older animals. For instance, periadolescents tend to show enhanced acquisition of simple active avoidance tasks, but impaired acquisition of more complex appetitive and aversive discriminations. In this experiment, rats were trained on a simple passive avoidance task at one of three ages, as weanlings (25 days), periadolescents (35 days), or young adults (45 days). Training occurred in the presence of both a redundant discriminative stimulus and a specified, redundant contextual stimulus. The periadolescents did not differ from either younger or older rats in rate of learning the passive avoidance task. The retention performance of these animals was then tested following a change in either, neither, or both of the redundant cues. When a measure of performance that controls for baseline activity was used, it was observed that periadolescents were not disrupted by a change in the redundant discriminative stimulus, a cue change that clearly disrupted performance in 25- and 45-day-old animals, and tended to be more disrupted by the contextual change than younger or older rats. It is hypothesized that the alterations in performance exhibited by periadolescents may be related to an ontogenetic alteration in stimulus selection modulated by the catecholaminergic systems.     

EVALUATION OF A TECHNIQUE FOR MEASURING SUBJECTIVE SIMILARITY

The purpose was to develop and test a scaling technique simple enough to be useful in developmental studies. The basic assumption was that consistent quantitative judgments can be obtained from children when the task is simply to place two stimuli in such a way that their spatial proximity corresponds to their subjective similarity. Children as young as six years were able to carry out the task consistently. The reliability of the technique was quite high with simple material and appeared satisfactory even when complex stimuli were scaled. Methods for analyzing the results are discussed. Factorization of the proximity matrices yielded the expected dimensions. Some pilot experiments are reported illustrating the use of the technique with complex stimulus materials.     

The effect of context on discrimination and bias in recognition memory for pictures and words

When the context accompanying a to-be-remembered word is changed between study and test, recognition memory is impaired. The deleterious effect of context change on recognition memory can be viewed as support for encoding specificity theory, semantic theory, or the existence of two bases for recognition. A fourth possible interpretation, examined here, is that the effect of context change on recognition memory is due to an accompanying change in response bias, rather than a "true" decrease in sensitivity to old and new items. In two experiments, the effect of context change on discrimination and bias in recognition of simple line drawings and their names was examined. Bias was measured using two measures shown by Snodgrass and Corwin (1988) to be theoretically independent of their associated discrimination measures. Context change produced marked conservatism in response bias in both experiments but demonstrated an effect on discrimination in the second experiment only. The shift from a neutral to a conservative response strategy as a result of context change may also be seen in other experiments, in which the same experimental paradigm was used with a variety of stimulus materials. We suggest that the major effect of context manipulation is to produce a change in bias. A stimulus in a familiar environment appears to be more familiar than a stimulus in a strange environment, regardless of its old/new status. In addition, there appears to be a true decrease in discrimination with context change, but this is more difficult to detect. The finding that pictures, which are less polysemous than words, are as affected by context change as words are supports encoding specificity theory over semantic theory.     

Neural responses to morphological, syntactic, and semantic properties of single words: an fMRI study

Dissociations in the recognition of specific classes of words have been documented in brain-injured populations. These include deficits in the recognition and production of morphologically complex words as well as impairments specific to particular syntactic classes such as verbs. However, functional imaging evidence for distinctions among the neural systems underlying these dissociations has been inconclusive. We explored the neural systems involved in processing different word classes in a functional Magnetic Resonance Imaging study, contrasting four groups of words co-varying morphological complexity (simple, monomorphemic words vs complex derived or inflected words) and syntactic class (verbs vs nouns/adjectives). Subtraction of word from letter string processing showed activation in left frontal and temporal lobe regions consistent with prior studies of visual word processing. No differences were observed for morphologically complex and simple words, despite adequate power to detect stimulus specific effects. A region of posterior left middle temporal gyrus showed significantly increased activation for verbs. Post hoc analyses showed that this elevated activation could also be related to semantic properties of the stimulus items (verbs have stronger action associations than nouns, and action association is correlated with activation). Results suggest that semantic as well as syntactic factors should be considered when assessing the neural systems involved in single word comprehension.     

The Effects of Selective Cholinergic Basal Forebrain Lesions and Aging upon Expectancy in the Rat

The effects of selective cholinergic cell loss within the basal forebrain (BF) were determined using a task that requires shifting of attention between two visual stimuli. Discriminability between two stimuli and response bias were determined in young and old F-344 rats given BF injections of IgG-192 saporin (100 ng). The lesion reduced ChAT activity in the frontal and parietal cortices, hippocampus, and olfactory bulbs. The lesion did not significantly alter Na⁺/K⁺-ATPase activity in cortex, hippocampus, or olfactory bulbs, or endogenous levels of neuropeptide Y and neurokinin B within the BF. The BF lesions impaired both stimulus discriminability and response bias in young and old rats. The BF lesions had a significantly greater effect upon stimulus discriminability and response bias in aged rats, compared to young rats, only when the stimulus duration was very brief, i.e., when the task was most difficult to solve. At longer stimulus durations, aging and lesions showed no interaction. The results suggest that the selective loss of cholinergic cells in the BF, but not normal aging, impairs the ability to discriminate between independent sensory stimuli. The loss of these cells confers a response bias in simple operant tasks involving motor responses to reward-related visual stimuli.     

Repetition effect with picture stimuli: Possible implications for clarity

Increasing recognition accuracy with repeated presentations was demonstrated for complex pictorial stimuli (real-world photographs) by accuracy, signal detection, and confidence of decision indicators. Consistent with other research, the effect occurred only for short stimulus durations. The effect occurred for both old and new pictures, the rate of improvement being greater for old than for new pictures. Experiment II utilized focus-degraded stimuli to demonstrate that amount of information artifacts were not responsible for the observed differences between responses to old and new pictures.     

错误再认:意识、注意和刺激特性

该研究基于错误再认现象,确立了意识知觉和无意识知觉在行为结果上的质的差异。在决定一个刺激是被有意识知觉还是无意识知觉时,刺激特性和注意之间存在着相互补偿的作用。实验一表明,当一个刺激短暂呈现而被无意识知觉的时候,增强刺激特性或提高注意水平都能使它的知觉变为有意识的;相对应地,实验二表明,一个处于分散注意条件下被无意识知觉的刺激,也可以通过使注意集中或增强刺激特性而使它的知觉变为有意识的。该研究对意识、注意和刺激特性三者间的关系进行了讨论。     

Simulation of associative learning with the replaced elements model

Associative learning theories can be categorized according to whether they treat the representation of stimulus compounds in an elemental or a configural manner. Since it is clear that a simple elemental approach to stimulus representation is inadequate, there have been several attempts to produce more elaborate elemental models. One recent approach, the replaced elements model (Wagner, 2003), reproduces many results that have until recently been uniquely predicted by Pearce's configural theory (Pearce, 1994). Although it is possible to simulate the replaced elements model using "standard" simulation programs, the generation of the correct stimulus representation is complex. The present article describes a method for simulation of the replaced elements model and presents the results of two example simulations that show differential predictions of replaced elements and Pearce's configural theory.     

Habituation, response to novelty, and dishabituation in human infants: tests of a dual-process theory of visual attention

Two experiments were conducted to test a dual-process theory of infants' performance on visual habituation-dishabituation tasks. The findings demonstrate that (a) infant habituation functions are often nonmonotonic, with fixation increasing before the eventual response waning; (b) this initial increment in responding is related to stimulus "complexity"; (c) response to novelty is enhanced by increasing the "complexity" of the novelty-test stimulus; and (d) dishabituation, followed by decay, occurs for familiarized patterns when retested after the introduction of a "complex" stimulus, but not after introduction of a "simple" stimulus. Following P. Groves and R. Thompson (1970, Psychological Review, 77, 419-450) we propose that infant visual attention to repeated presentations of a stimulus involves two processes, habituation and sensitization.     

A moving video window or mask yoked to eye movements: A system to permit free ocular scanning within delimited areas of the visual field

A system is described for generating a video window or mask that is yoked to a subject’s eye movements and that can be used to mask off either the left or the right visual field, while still permitting prolonged examination of simple or complex visual stimuli. It can also be used to simulate various visual field defects or scotomata and to ensure that subjects maintain fixation during extended stimulus presentations. Circuitry is provided, and two additional options are suggested.     

3.5~5.5岁儿童在知觉相似与概念冲突情形下的归纳推理

了探讨儿童是基于知觉相似的还是基于概念的进行归纳推理的,利用儿童较为熟悉的材料,设计了一种知觉相似与概念冲突的情形,并在4种不同的信息提示条件下,测试了总共275名3.5岁、4.5岁和5.5岁儿童的归纳推理。实验结果显示,在预备实验中,3.5岁的儿童已经能够排除无关刺激要么基于知觉相似要么基于概念进行归纳推理,但二者没有显著差异;在正式实验中,在4种任务条件下,3.5岁的儿童的情况基本与预备实验相同,而4.5岁和5.5岁的儿童则更倾向于基于概念进行归纳推理,这表明儿童的归纳推理可能的确经历了从依据知觉相似到依据概念关系的转变,但发生转变的年龄应该不是在7~8岁,而是在4岁之前     

Perception of depth: Different processing times for simple and relative positional disparity

Summary When judging in stereoscopic vision whether an object is lying in front of or behind the point of momentary fixation, the visual system extracts depth information by using retinal disparity; in this case it computes one angular difference between retinal images (simple positional disparity). But if the task is to discriminate two or more objects in their depth (relative to the point of fixation) and the relative distances between them, two or more such angular differences have to be determined (relative positional disparity). An investigation was carried out to determine whether depth extraction is more complex for relative distances than for object positions and therefore demands a longer processing time. For this purpose stimuli with simple and relative positional disparity were foveally and parafoveally presented (each followed by a masking stimulus). It was shown that the duration threshold for the detection of stimuli with relative disparity was about 2.5 times larger than that for stimuli with simple disparity (Exp. 1). This difference could not be attributed to differences in stimulus configuration between simple and relative disparity (Exp. 2). The results are discussed in terms of a serial, hierarchically structured, disparity processing.     

Identification of the eye-brain-hand system with point processes: a new approach to simple reaction time

By presenting a Poisson process of flashes to observers who hit a button as quickly as possible after each, the authors identified the system involved in simple reaction time (RT). The nonlinear kernels up to 2nd order were measured from the stimulus and response point processes. The 1st-order kernel is analogous to a histogram of simple RTs. The 2nd-order kernel shows complex patterns of nonlinear suppression and facilitation between pairs of flashes. Simple RT measured as the lag of the 1st-order kernel's peak agrees with RT from conventional discrete trial experiments. RTs are shorter and less variable when the flashes are separated by uniform rather than exponential delays, which shows that observers use the stimulus hazard function to become prepared to detect and respond to the flash.