Negative priming and perceptual fluency: More than what meets the eye

In two priming experiments, we manipulated the perceptual quality of the target or the distractor on the prime trial; the stimuli were repeated or novel. Negative priming was found to be contingent on stimulus repetition, because it was obtained with repeated items but not with novel items. Prime trial perceptual degradation modulated negative priming for repeated items but had no effect on priming in ignored repetition conditions using novel stimuli. These patterns were obtained even when the effect of perceptual degradation was (1) greater than the effect of stimulus repetition and (2) greater for novel words than for repeated words. Although stimulus repetition increases perceptual fluency, the activation of perceptual representations by itself is not sufficient to produce negative priming. Instead, we suggest that negative priming is a manifestation of an activation-sensitive inhibitory mechanism that functions to reduce response competition.     

Negative priming and perceptual fluency: more than what meets the eye

In two priming experiments, we manipulated the perceptual quality of the target or the distractor on the prime trial; the stimuli were repeated or novel. Negative priming was found to be contingent on stimulus repetition, because it was obtained with repeated items but not with novel items. Prime trial perceptual degradation modulated negative priming for repeated items but had no effect on priming in ignored repetition conditions using novel stimuli. These patterns were obtained even when the effect of perceptual degradation was (1) greater than the effect of stimulus repetition and (2) greater for novel words than for repeated words. Although stimulus repetition increases perceptual fluency, the activation of perceptual representations by itself is not sufficient to produce negative priming. Instead, we suggest that negative priming is a manifestation of an activation-sensitive inhibitory mechanism that functions to reduce response competition.     

Behavioral evidence for format-dependent processes in approximate numerosity representation

A genuinely abstract number representation is thought to be capable of representing the numerosity of any set of discrete elements, whether they are sequentially or simultaneously presented. Recent neuroimaging studies, however, have demonstrated that different areas of intraparietal sulcus play a role in extracting numerosity across simultaneous or sequential presentation during a quantification process, suggesting the existence of a format-dependent numerical system. To test whether behavioral evidence exists for format-dependent numerical processing in adult humans, we measured the Weber fractions of numerosity discrimination for sequential stimuli, simultaneous stimuli, and cross-format stimuli with a carefully controlled experimental procedure. The results showed distinct differences between the performance in the simultaneous and sequential conditions, supporting the existence of format-dependent processes for numerosity representation. Moreover, the performance on cross-format trials differed among participants, with the exception that performance was always worse than in the simultaneous condition. Taken together, our findings suggest that numerical representation may involve a complex set of multiple stages.     

保留的跨通道启动与老化：对于近期观点的总结

通道内重复启动的研究提示老年人内隐记忆未受损, 这不只体现在视觉通道上还包括其他感觉通道(例如触觉、听觉和嗅觉)。然而很少有研究考察启动任务是否具有通道特异性。在以年轻人为被试的研究中发现跨通道迁移(视觉到触觉和触觉到视觉)和通道内迁移(视觉到视觉, 触觉到触觉)具有相似性。一项最近的研究进一步探索老年人在跨通道启动任务上是否受损。结果显示视觉和触觉间的跨通道启动在年轻被试和老年被试上都是保留的且具有对称性。并且, 对于自然声响、图片的通道内和跨通道启动任务随着年老化发展仍旧保留。这些行为结果和其它最近神经科学结果显示跨通道启动发生于枕叶后纹状皮层区, 而这一区域在老年人中未损坏。这一领域未来的研究方向包括利用不同知觉通道间、利用熟悉的和新异的刺激并结合行为的和脑成像的方法, 通过设计完善的跨通道启动来研究正常老人与阿尔兹海默病人, 还包括将设计得完善的启动任务包括在用于改善老年人记忆功能的项目中。     

An Item specific Locus of Repetition Priming

Two principal types of account of repetition priming postulate either facilitation of activation of perceptual representations used in stimulus recognition, or retrieval of specific processing episodes as possible mechanisms by which the effect occurs; these make different predictions concerning the priming of two stimuli presented simultaneously. In Experiments 1-3, subjects made same/different decisions about picture-word stimulus pairs. Recombining the pairings of a subset of items between training and test encounters did not significantly reduce the benefit in response time from repetition, as compared to pairs repeated intact. Subjects were able to remember the pairings (Experiment 4), but this did not influence repetition priming. Instead, the memory representations underlying the priming of each item in a pair were independent. No priming was found between pictures seen at training and words at test, and vice versa (Experiment 5), indicating that representations underlying the repetition effect were domain-specific. In Experiment 6, stimuli were all from within the domain of object pictures. Again, recombining the pairings of items between training and test did not significantly reduce the benefit in response time from repetition, as compared to pairs repeated intact. These results reveal an item-specific locus for repetition priming, consistent with priming occurring within pre-semantic perceptual representation systems involved in item recognition. The findings pose problems for theories that argue that repetition effects result only from retrieval of entire processing episodes.     

Response-mediated spatial priming despite perfectly valid target location cues and intervening response events

Attentional effects are often inferred from keypress reaction time (RT) studies when two sequentially presented stimuli, appearing at the same location, generate costs or benefits. The universality of these attentional attributions is challenged by data from perceptual discrimination tasks, which reveal that location repetition benefits and costs depend on whether a prior response repeats or switches, respectively. According to dual-stage accounts, these post-attentional effects may be abolished by making responses in between two target stimuli or by increasing target location certainty, leaving only attentional effects. Here, we test these accounts by requiring responses to stimuli in between targets and by increasing target location certainty with 100% valid location cues. Contrary to expectations, there was no discernible effect of cueing on any repetition effects, although the intervening response diminished stimulus-response repetition effects while subtly reducing location-response repetition effects. Despite this, there was little unambiguous evidence of attentional effects independent of responding. Taken together, the results further highlight the robustness of location-response repetition effects in perceptual discrimination tasks, which challenge whether there are enduring attentional effects in this paradigm.     

Age differences in implicit memory: conceptual, perceptual, or methodological?

The authors examined age differences in conceptual and perceptual implicit memory via word-fragment completion, word-stem completion, category exemplar generation, picture-fragment identification, and picture naming. Young, middle-aged, and older participants (N = 60) named pictures and words at study. Limited test exposure minimized explicit memory contamination, yielding no reliable age differences and equivalent cross-format effects. In contrast, explicit memory and neuropsychological measures produced significant age differences. In a follow-up experiment, 24 young adults were informed a priori about implicit testing. Their priming was equivalent to the main experiment, showing that test trial time restrictions limit explicit memory strategies. The authors concluded that most implicit memory processes remain stable across adulthood and suggest that explicit contamination be rigorously monitored in aging studies.     

The subliminal mere exposure effect does not generalize to structurally related stimuli.

R.F. Bornstein (1994) questioned whether subliminal mere exposure effects might generalize to structurally related stimuli, thereby providing evidence for the existence of implicit learning. Two experiments examined this claim using letter string stimuli constructed according to the rules of an artificial grammar. Experiment 1 demonstrated that brief, masked exposure to grammatical strings impaired recognition but failed to produce a mere exposure effect on novel structurally related strings seen at test. Experiment 2 replicated this result but also demonstrated that a reliable mere exposure effect could be obtained, provided the same grammatical strings were presented at test. The results suggest that the structural relationship between training and test items prevents the mere exposure effect when participants are unaware of the exposure status of stimuli, and therefore provide no evidence for the existence of implicit learning.     

Generate and test: An alternative route to knowledge elicitation in an implicit learning task

Three experiments are reported, which examine generation of knowledge in the McGeorge and Burton (1990) invariant learning task. In this task, participants are exposed to 30 four-digit numbers containing an invariant "3". Following this participants then demonstrate a preference for novel numbers containing this invariant over numbers without it. Despite above-chance performance on this pseudo-memory test, participants appear unable to verbalize anything pertinent to the invariant. Here we introduce a novel version of this task, relying on generation of items rather than a preference test. We argue that this new task engages different processing resources, resulting in different patterns of performance. In Experiment 1, invariant learning was demonstrated using a novel fragment completion test. Experiment 2 found that suppressing articulation inhibited learning, implying that this test task accesses phonological knowledge. It is suggested that using the fragment completion test engages different processing resources during test from those in a preference test. Experiment 3 reinforces this position by demonstrating that knowledge appears to transfer across surface features, a result that seems to contradict recent findings by Stadler, Warren, and Lesch (2000). A resolution is offered, drawing on episodic accounts of implicit learning.     

The role of variation in the perception of accented speech

Phonetic variation has been considered a barrier that listeners must overcome in speech perception, but has been proved beneficial in category learning. In this paper, I show that listeners use within-speaker variation to accommodate gross categorical variation. Within the perceptual learning paradigm, listeners are exposed to p-initial words in English produced by a native speaker of French. Critically, listeners are trained on these words with either invariant or highly-variable VOTs. While a gross boundary shift is made for participants exposed to the variable VOTs, no such shift is observed after exposure to the invariant stimuli. These data suggest that increasing variation improves the mapping of perceptually mismatched stimuli.     

Speech perception and memory coding in relation to reading ability

Previous work has demonstrated that children who are poor readers have short-term memory deficits in tasks in which the stimuli lend themselves to phonetic coding. The aim of the present study was to explore whether the poor readers' memory dificit may have its origin in perception with the encoding of the stimuli. Three experiments were conducted with third grade good and poor readers. As in earlier experiments, the poor readers were found to perform less well on recall of random word strings and to be less affected by the phonetic characteristics (rhyming or not rhyming) of the items (Experiment 1). In addition, the poor readers produced more errors of transposition (in the nonrhyming strings) than did the good readers, a further indication of the poor readers' problems with memory for order. The subjects were tested on two auditory perception tasks, one employing words (Experiment 2) and the other nonspeech environmental sounds (Experiment 3). Each was presented under two conditions: with a favorable signal-to-noise ratio and with masking. The poor readers made significantly more errors than the good readers when listening to speech in noise, but did not differ in perception of speech without noise or in perception of nonspeech environmental sounds, whether noise-masked or not. Together, the results of the perception studies suggest that poor readers have a perceptual difficulty that is specific to speech. It is suggested that the short-term memory deficits characteristic of poor readers may stem from material-specific problems of perceptual processing.     

Inducing the familiarity effect

The task required subjects to judge whether members of six-letter consonant string pairs were physically identical. Some (repeated) strings were presented on each of the 16 training sessions, while other (nonrepeated) strings were presented only during a single session. An advantage in matching time of repeated strings over nonrepeated strings was obtained which increased in a roughly linear fashion during training and which persisted for at least 7 weeks after the last training session. Detailed analyses of thedifferent responses and the results of several transfer tasks suggest that perceptual processing is indeed facilitated by acquired information about which letters usually follow others and about the positions in which these sequences of letters are likely to occur, but provide no evidence that this facilitation derives from the formation of visual features which are larger than single letters.     

Electrophysiological evidence for size invariance in masked picture repetition priming

This experiment examined invariance in object representations through measuring event-related potentials (ERPs) to pictures in a masked repetition priming paradigm. Pairs of pictures were presented where the prime was either the same size or half the size of the target object and the target was either presented in a normal orientation or was a normal sized mirror reflection of the prime object. Previous masked repetition priming studies have found a cascade of priming effect sensitive to perceptual (N190/P190) and semantic (N400) properties of the stimulus. This experiment found that both early (N190/P190 effects) and later effects (N400) were invariant to size, whereas only the N190/P190 effect was invariant to mirror reflection. The combination of a small prime and a mirror reflected target led to no significant priming effects. Taken together, the results of this set of experiments suggests that object recognition, more specifically, activating an object representation, occurs in a hierarchical fashion where overlapping perceptual information between the prime and target is necessary, although not always sufficient, to activate a higher level semantic representation.     

Implicit learning modulates selective attention at sensory levels of perceptual processing

Electrophysiological evidence suggests that attention can be modulated as early as 100 msec after stimulus presentation. However, it is not clear whether these changes are based primarily on stimulus properties such as perceptual load (i.e., the level of perceptual difficulty), or other properties, such as general attentional set or learned expectations concerning perceptual load. Using event-related potentials, this study examined how implicit learning of perceptual load conditions modulates selective attention at sensory levels of perceptual analysis. The results show significant differences in P1 amplitude recorded over occipital areas of the brain as a function of learned expectations of perceptual load, only when perceptual load could be reliably predicted by the preceding stimuli. Moreover, differences in processing were found when both low and high perceptual load conditions could be predicted. These findings suggest that implicit learning modulates the allocation of attention at early stages of perceptual processing.     

Selective auditory grouping by zebra finches: testing the iambic–trochaic law

Humans have a strong tendency to spontaneously group visual or auditory stimuli together in larger patterns. One of these perceptual grouping biases is formulated as the iambic/trochaic law, where humans group successive tones alternating in pitch and intensity as trochees (high–low and loud–soft) and alternating in duration as iambs (short–long). The grouping of alternations in pitch and intensity into trochees is a human universal and is also present in one non-human animal species, rats. The perceptual grouping of sounds alternating in duration seems to be affected by native language in humans and has so far not been found among animals. In the current study, we explore to which extent these perceptual biases are present in a songbird, the zebra finch. Zebra finches were trained to discriminate between short strings of pure tones organized as iambs and as trochees. One group received tones that alternated in pitch, a second group heard tones alternating in duration, and for a third group, tones alternated in intensity. Those zebra finches that showed sustained correct discrimination were next tested with longer, ambiguous strings of alternating sounds. The zebra finches in the pitch condition categorized ambiguous strings of alternating tones as trochees, similar to humans. However, most of the zebra finches in the duration and intensity condition did not learn to discriminate between training stimuli organized as iambs and trochees. This study shows that the perceptual bias to group tones alternating in pitch as trochees is not specific to humans and rats, but may be more widespread among animals.     

Typing letter strings varying in orthographic structure

Subjects typed six-letter strings varying in orthographic structure. Lexical status, word frequency, position-sensitive log bigram frequency, and regularity of letter sequencing were systematically varied. Cumulative reaction times (RTs) of the keystrokes were adequately described by a linear function of letter position in the test string. Overall, words were typed faster than nonwords, and regular strings faster than irregular strings. Although the effect of log bigram frequency was not significant, this variable interacted with regularity and word frequency. Post hoc analyses of performance on each of the 200 letter strings revealed significant effects of the number of irregularities, log bigram frequency, and log word frequency. Transition times between successive keystrokes were significantly longer for illegal than for legal letter transitions. These results are similar to previous findings on the role of orthographic structure in the perceptual recognition of letter strings and provide a more complete analysis of context effects in typing.     

Sequential analysis of the numerical Stroop effect reveals response suppression

Automatic processing of irrelevant stimulus dimensions has been demonstrated in a variety of tasks. Previous studies have shown that conflict between relevant and irrelevant dimensions can be reduced when a feature of the irrelevant dimension is repeated. The specific level at which the automatic process is suppressed (e.g., perceptual repetition, response repetition), however, is less understood. In the current experiment we used the numerical Stroop paradigm, in which the processing of irrelevant numerical values of 2 digits interferes with the processing of their physical size, to pinpoint the precise level of the suppression. Using a sequential analysis, we dissociated perceptual repetition from response repetition of the relevant and irrelevant dimension. Our analyses of reaction times, error rates, and diffusion modeling revealed that the congruity effect is significantly reduced or even absent when the response sequence of the irrelevant dimension, rather than the numerical value or the physical size, is repeated. These results suggest that automatic activation of the irrelevant dimension is suppressed at the response level. The current results shed light on the level of interaction between numerical magnitude and physical size as well as the effect of variability of responses and stimuli on automatic processing.     

Priming and stimulus-response learning in perceptual classification tasks

Participants often respond more quickly and more accurately to a repeated stimulus compared to a non-repeated one, a phenomenon known as repetition priming. In semantic classification tasks priming appears to be largely attributable to the learning of stimulus-decision and stimulus-response associations, which allow participants to bypass many of the processes engaged during initial stimulus analysis. The current study tested whether stimulus-response learning plays a similarly dominant role in priming that occurs in perceptual classification tasks. Unfamiliar objects were used as stimuli to reduce the influence of semantic processes on priming and the task switched for all test trials to eliminate stimulus-decision learning. The results showed across-task priming as measured by reaction time facilitation and improved accuracy when the response remained the same during the encoding and test phases. When the response switched, similar levels of reaction time facilitation were observed, but priming as measured by accuracy was significantly reduced and no longer significant. These findings indicate that stimulus-response learning contributes to priming in perceptual classification tasks, but does not play a dominant role. Significant stimulus-level learning that is independent of the task and response also occurs and likely indexes facilitated perceptual processing of the objects.     

Functional MRI evidence for an abstract, not perceptual, word-form area

Previous studies have found an area in left ventral visual cortex that responds more to words and pseudowords than to consonant strings. Does this area respond to the perceptual form of wordlike stimuli, or is it responding to some more abstract, linguistic property, such as orthographic regularity (i.e., conformity with the spelling rules of the language)? During a functional magnetic resonance imaging experiment, participants read alternating-case words and pseudowords, which are orthographically regular but are perceptually unfamiliar. These stimuli activated the same area that was activated by pure-case words and pseudowords. These results suggest that the response of the so-called word-form area is not based on perceptual familiarity but rather on some more abstract feature such as orthographic regularity.     

When perceptual or motor sets are changed: Effects of updating demands on structure and energy of P300

It was attempted to disentangle the effect of two updating processes on P300. Three conditions were created by a priming paradigm: (1) No updating, (2) updating perceptual but no motor information, and (3) updating both perceptual and motor information. As expected, both updating conditions led to a P300-complex with more energy, but the additional demand of motor updating did not affect P300. Effects were similar for both delayed (experiment 1) and immediate responding (experiment 2).

Both experiments confirmed earlier observations that P300 consists of at least three subcomponents, namely P3a, P3b, and a positive Slow Wave (pSW). Perceptual updating affected in particular the energy of P3b and pSW. Further, pSW was related to the complexity of the updating operations. When stimuli consisted of abstract symbols there was more energy in pSW than when stimuli were concrete symbols with direct spatial relations to the response.

The structure and energy changes of P300 suggest that P3b and pSW do not provide an unambiguous picture of the underlying source structure. In some conditions only one peak (P3b) was observed in the surface structure; this still seemed to be the result of two underlying waves. In other conditions these waves were separated in time showing a clear double peak in the surface structure.