The ghosts of brain states past: Remembering reactivates the brain regions engaged during encoding.

There is growing evidence that the brain regions involved in encoding an episode are partially reactivated when that episode is later remembered. That is, the process of remembering an episode involves literally returning to the brain state that was present during that episode. This article reviews studies of episodic and associative memory that provide support for the assertion that encoding regions are reactivated during subsequent retrieval. In the first section, studies are reviewed in which neutral stimuli were associated with different modalities of sensory stimuli or different valences of emotional stimuli. When the neutral stimuli were later used as retrieval cues, relevant sensory and emotion processing regions were reactivated. In the second section, studies are reviewed in which participants used different strategies for encoding stimuli. When the stimuli were later retrieved, regions associated with the different encoding strategies were reactivated. Together, these studies demonstrate not only that the encoding experience determines which regions are activated during subsequent retrieval but also that the same regions are activated during encoding and retrieval. In the final section, relevant questions are posed and discussed regarding the reactivation of encoding regions during retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The psychobiological basis of posttraumatic stress disorder

Posttraumatic stress disorder is a disorder with an identifiable etiological factor (exposure to a traumatic event) and with a complex symptomatology (i.e. intrusive memories, avoidance, hyperarousal) that suggests dysfunction in multiple psychobiological systems. This review considers studies of the neurobiological consequences of acute and chronic stress showing that traumatic experiences can produce long-lasting alterations in multiple neurochemical systems. The role of the locus coeruleus noradrenergic system, prefrontal cortex dopaminergic system, endogenous opiates, hypothalamic-pituitary-adrenal axis, and cortico-releasing factors are reviewed. Several models of PTSD are highlighted, including fear conditioning, kindling, and sensitization. In particular, fear conditioning to explicit and contextual cues is proposed as a model for intrusive memories reactivated by trauma-related stimuli and hyperarousal, respectively. It is argued that the amygdala plays a crucial role in the encoding and retrieval of fear memories activated by specific stimuli that have been associated with aversive events. Association involving more complex environmental stimuli and aversive events may require the involvement of the hippocampus and the bed nucleus of the stria terminalis. Repeated activation of conditioned fear memories may produce a kindling-like process which results in spontaneous intrusive memories.     

"The acquisition of task-specific productions and modification of declarative representations in spatial-precuing tasks": Correction to Proctor and Reeve.

Reports an error in "The acquisition of task-specific productions and modification of declarative representations in spatial-precuing tasks" by Robert W. Proctor and T. Gilmour Reeve (Journal of Experimental Psychology: General, 1988[Jun], Vol 117[2], 182-196). The spanner heads were inadvertently omitted from Tables 2 and 3 and Tables 6 and 7. The four tables are reprinted in the erratum. (The following abstract of the original article appeared in record 1988-28565-001.) Three experiments explored the role of the stimulus–response translation stage of human information processing in relating stimuli to assigned responses. The primary findings are that (a) task-specific productions develop with practice that relate stimuli directly to specific fingers, and (b) declarative knowledge is acquired that can lead to the use of modified representations when translation subsequently is required in a transfer session. The results are consistent with the view that the mediating role of the translation stage decreases with practice and is inconsistent with the view that the role does not change or diminish. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representations of the magnitudes of fractions.

We tested whether adults can use integrated, analog, magnitude representations to compare the values of fractions. The only previous study on this question concluded that even college students cannot form such representations and instead compare fraction magnitudes by representing numerators and denominators as separate whole numbers. However, atypical characteristics of the presented fractions might have provoked the use of atypical comparison strategies in that study. In our 3 experiments, university and community college students compared more balanced sets of single-digit and multi-digit fractions and consistently exhibited a logarithmic distance effect. Thus, adults used integrated, analog representations, akin to a mental number line, to compare fraction magnitudes. We interpret differences between the past and present findings in terms of different stimuli eliciting different solution strategies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reactivation of nonassociative memory

The orienting response to an auditory stimulus, as measured by a decrease in heart rate, habituates rapidly, and at the same rate in preweanling and adult rats. Although adult rats retain this nonassociative memory for at least 7 days, preweanling rats show extremely rapid forgetting. In the preweanling, forgetting of this nonassociative memory appears to be complete after just 24 hr (Richardson & Campbell, 1991b). The results of several experiments in the present study with preweanling rats demonstrated that this type of nonassociative memory could be reactivated by presenting a fractional component of the original eliciting stimulus just prior to testing. The effectiveness of the reactivation treatment was critically dependent upon both the number of reactivating stimuli presented and the duration of those stimuli. Reactivation was also found to be stimulus-specific in that presentation of an auditory stimulus qualitatively different from that used in training (white noise instead of a pure tone) did not reactivate the memory. Control groups in each experiment demonstrated that the reactivation treatment facilitated retrieval of the prior nonassociative memory and did not produce new learning. A possible process through which nonassociative memories can be reactivated is discussed.     

Mental rotation of representations of two-dimensional and three-dimensional objects.

Empirical and theoretical considerations suggest that representations of three-dimensional objects should be more difficult to rotate mentally than representations of two-dimensional objects. In this study, subjects were asked to make mirror-normal decisions with stimuli that differed in perceived dimensionality and in angle of rotation in the image plane. In a series of four experiments, the time to make mirror-normal decisions increased with increased orientation discrepancy between the stimuli, as found previously in the literature. In every experiment, however, response times were smaller for representations of two-dimensional shapes than for representations of three-dimensional shapes when the stimuli being compared were presented with a large angular discrepancy. Whereas response times increased linearly with orientation when representations of three-dimensional shapes were rotated, the increase in response time for representations of two-dimensional shapes was generally nonlinear. Overall, the evidence suggests that representations of three-dimensional shapes are mentally rotated at the same rate as representations of two-dimensional shapes for angles of rotation between 0° and 60°. For larger angles of rotation, however, the rate of mental rotation is greater for representations of two-dimensional shapes than for representations of three-dimensional shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic mental representations.

This article pursues the possibility that perceivers are sensitive to implicit dynamic information even when they are not able to observe real-time change. Recent empirical results in the domains of handwriting recognition and picture perception are discussed in support of the hypothesis that perception involves acquiring information about transitions, whether the stimuli are static or dynamic. It is then argued that dynamic information has a special status in mental representation as well as in perception. In particular I propose that some mental representations may be dynamic, in that a temporal dimension is necessary to the representation. Recent evidence that mental representations may exhibit a form of momentum is discussed in support of this claim. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Understanding pictures and words: Comment on Potter, Kroll, Yachzel, Carpenter, and Sherman (1986).

Although pictures are named more slowly than words, some meaning judgments can be made as quickly for both classes of stimuli. This finding has been taken as evidence that a common, conceptual system underlies the meaning of pictures and words. The results are also consistent, however, with a dual coding theory of meaning that postulates only modality-specific imaginal and verbal representations for pictures and words, respectively. The equal accessibility of words and pictures to some aspects of meaning is explained by diverse connections among the representations or by modality-specific components of meaning rather than by conceptual representations, which are actually unnecessary to explain the phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of directed attention in the human extrastriate cortex as revealed by functional MRI

A typical scene contains many different objects, but the capacity of the visual system to process multiple stimuli at a given time is limited. Thus, attentional mechanisms are required to select relevant objects from among the many objects competing for visual processing. Evidence from functional magnetic resonance imaging (MRI) in humans showed that when multiple stimuli are present simultaneously in the visual field, their cortical representations within the object recognition pathway interact in a competitive, suppressive fashion. Directing attention to one of the stimuli counteracts the suppressive influence of nearby stimuli. This mechanism may serve to filter out irrelevant information in cluttered visual scenes.     

Does orientation-independent object recognition precede orientation-dependent recognition? Evidence from a cuing paradigm.

Object recognition may entail an incremental normalization process before access to canonical orientation representations, but is this process guided by prior access to object-centered representations? In Exp 1, the authors showed observers figure–ground stimuli known to reflect access to, and output from, stored shape representations. The stimuli appeared in each of 6 different orientations, preceded by cues providing either (1) no information, (2) upright shape information only, (3) upright shape information plus orientation information (separately), or (4) shape information in the same orientation as the upcoming figure–ground test stimulus. Contrary to predictions by a postaccess account, the cues failed to eliminate orientation dependency in shape recognition. Results favor a preaccess account of the normalization process within the context of canonical orientation representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Severity of experimentally reactivated herpetic eye disease is related to the neurovirulence of the latent virus

The authors examined the eye diseases produced during acute and experimentally reactivated infections of rabbits intranasally inoculated with high and low neurovirulent strains of herpes simplex virus, type-1 (HSV-1). Experimental reactivation of latent trigeminal ganglionic infection was accomplished by an injection of cyclophosphamide followed by one injection of dexamethasone the next day. Neither drug, when given as a single injection, reactivated latent HSV-1 infection. During acute and reactivated phases of high neurovirulent HSV-1 strain infection, many rabbits developed very severe conjunctivitis and keratitis. Some rabbits developed hemorrhagic corneal lesions, and a few became blind. Only a few rabbits with acute and reactivated low neurovirulent virus strain infections developed mild conjunctivitis. The high neurovirulent strain was recovered from tear film more frequently than the low neurovirulent strain during reactivated infections. By use of 3H-labelled DNA prepared from purified virus to probe trigeminal ganglionic tissues in situ, both strains of virus were found to establish ganglionic latency to about the same degree. Reactivation correlated with an increase in the amount of HSV-1 RNA per ganglionic neuron and a change in subcellular location. These studies indicate that the relative neurovirulence of the infecting strain determines the ease with which it can be reactivated from latency and the severity of the reactivated ocular disease produced.     

Attention-referenced visual representations: Evidence from impaired visual localization.

Spatial representations in the visual system were probed in 4 experiments involving A. H., a woman with a developmental deficit in localizing visual stimuli. Previous research (M. McCloskey et al., 1995) has shown that A. H.'s localization errors take the form of reflections across a central vertical or horizontal axis (e.g., a stimulus 30° to her left localized to a position 30° to her right). The present experiments demonstrate that A. H.'s errors vary systematically as a function of where her attention is focused, independent of how her eyes, head, or body are oriented, or what potential reference points are present in the visual field. These results suggest that the normal visual system constructs attention-referenced spatial representations, in which the focus of attention defines the origin of a spatial coordinate system. A more general implication is that some of the brain's spatial representations take the form of coordinate systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrast discrimination, non-uniform patterns and change blindness

Change blindness--our inability to detect large changes in natural scenes when saccades, blinks and other transients interrupt visual input--seems to contradict psychophysical evidence for our exquisite sensitivity to contrast changes. Can the type of effects described as 'change blindness' be observed with simple, multi-element stimuli, amenable to psychophysical analysis? Such stimuli, composed of five mixed contrast elements, elicited a striking increase in contrast increment thresholds compared to those for an isolated element. Cue presentation prior to the stimulus substantially reduced thresholds, as for change blindness with natural scenes. On one hand, explanations for change blindness based on abstract and sketchy representations in short-term visual memory seem inappropriate for this low-level image property of contrast where there is ample evidence for exquisite performance on memory tasks. On the other hand, the highly increased thresholds for mixed contrast elements, and the decreased thresholds when a cue is present, argue against any simple early attentional or sensory explanation for change blindness. Thus, psychophysical results for very simple patterns cannot straightforwardly predict results even for the slightly more complicated patterns studied here.     

Electrophysiological evidence for a shared representational medium for visual images and visual percepts.

Systematic effects of imagery on visual signal detection performance have been used to argue that imagery and the perceptual processing of stimuli interact at some common locus of activity (Farah, 1985). However, such a result is neutral with respect to the question of whether the interaction occurs during modality-specific visual processing of the stimulus. If imagery affects stimulus processing at early, modality-specific stages of stimulus representation, this implies that the shared stimulus representations are visual, whereas if imagery affects stimulus processing only at later, amodal stages of stimulus representation, this implies that imagery involves more abstract, postvisual stimulus representations. To distinguish between these 2 possibilities, we repeated the earlier imagery-perception interaction experiment while recording event-related potentials (ERPs) to stimuli from 16 scalp electrodes. By observing the time course and scalp distribution of the effect of imagery on the ERP to stimuli, we can put constraints on the locus of the shared representations for imagery and perception. An effect of imagery was seen within 200 ms following stimulus presentation, at the latency of the 1st negative component of the visual ERP, localized at the occipital and posterior temporal regions of the scalp, that is, directly over visual cortex. This finding supports the claim that mental images interact with percepts in the visual system proper and hence that mental images are themselves visual representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple learning parameters differentially regulate olfactory generalization.

Sensory representations depend strongly on the descending regulation of perceptual processing. Generalization among similar stimuli is a fundamental cognitive process that defines the extent of the variance in physical stimulus properties that becomes categorized together and associated with a common contingency, thereby establishing units of meaning. The olfactory system provides an experimentally tractable model system in which to study the interactions of these physical and psychological factors within the framework of their underlying neurophysiological mechanisms. The authors here show that olfactory associative learning systematically regulates gradients of odor generalization. Specifically, increasing odor-reward pairings, odor concentration, or reward quality--each a determinant of associative learning--significantly transformed olfactory generalization gradients, each narrowing the range of variance in odor quality perceived as likely to share the learned contingency of a conditioned odor stimulus. However, differences in the qualitative features of these three transformations suggest that these different determinants of learning are not necessarily theoretically interchangeable. These results demonstrate that odor representations are substantially shaped by experience and descending influences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional capture by abrupt onsets: New perceptual objects or visual masking?

The authors have shown that an object appearing abruptly in a previously blank location is efficiently detected in visual search when it is embedded in an array of objects without abrupt onset (termed no-onset stimuli). In these experiments, no-onset stimuli appeared well before the onset stimulus but were camouflaged by additional line segments rendering the stimuli unidentifiable. B. S. Gibson (see record 1997-06229-001) claims that the availability of the no-onset stimuli was delayed relative to that of the abrupt onset stimulus because of forward masking. The authors show that forward masking is unlikely to be a significant factor in their experiments, and 3 new experiments are reported that undermine Gibson's masking account. Observed differences in the efficiency with which onset and no-onset stimuli are processed in visual search are due to attentional capture by new perceptual objects and to a relatively sluggish process of updating existing object representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reprèsentations verbales et transformations des stimulus en mémoire de travail.

During their storage in episodic memory, representations of words (or of other stimuli already known to Ss) can be transformed in working memory into representations of other words or stimuli by the application of transformation rules. In that way, items that have not been presented in learning lists can be recalled or recognized. Four experiments were conducted to induce these transformations by means of appropriate cues provided to 12–18 yr olds at the same time as the learning lists stimuli. The presence of those cues influenced recall and recognition significantly in comparison with control situations without cues; in particular, Ss recognized not-presented items corresponding to induced transformations of the stimuli presented. It is assumed that such operations may go with the item's retrieval from the mental lexicon. This possibility would provide an important functional argument in favor of the mental lexicon organization in the form of generic entries from which words could be derived by the application of rules similar to those studied in the present experiment. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of imagery-perception interaction.

A number of different research findings have shown that mental imagery can affect the perceptual processing of stimuli. The present research was aimed at characterizing the representations and processes underlying imagery–perception interactions. In 4 experiments, Ss mentally projected images of letters into the visual field, and either detected or detected and localized point threshold stimuli that fell on or off the image. Stimuli falling on the image were detected more often than stimuli falling off the image, consistent with the hypothesis that the representations at the interface between imagery and perception have an array format. When the facilitation was analyzed in terms of signal detection theory, it was found to consist only of criterion lowering, and not of enhanced sensitivity. The local criterion-lowering effect of imaged letters was then compared with the effect of perceiving a letter and attending to a letter. Perceiving a letter had no discernible effect on stimulus detection, whereas attending to the letter caused the same local criterion lowering, without sensitivity changes, as imaging the letter. This is consistent with the claims of U. Neisser (1976) and others that imagery is an attentional state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Varieties of size-specific visual selection.

Compared time to evaluate stimuli of varying sizes. When Ss expect an upcoming stimulus to be a certain size, response time increases with the disparity between expected and actual size. There are, however, 2 size adjustment processes, and they reflect 2 types of visual selection. In the first, a shape-specific image representation is used to separate a visual object from a superimposed distractor. These representations require the type of slow size scaling demonstrated in imagery experiments. The second size scaling process is faster and not shape-specific. At any given time the visual system is set to process information at a particular scale, and that scale can be adjusted to match an object's size. Because both selection mechanisms depend on size, they probably occur at a relatively low, spatially organized processing level. These findings lead to a new explanation for results that had been taken as evidence for attentional selection at the level of object representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of natural sensory factors in organization of feeding behavior using fledgling development as an example

A change in the composition of natural sensory stimuli, triggers of the alimentary functional system of Muscicapa hypoleuca nestlings, was studied throughout their nest life. In the first five days the alimentary reaction is elicited by a complex of acoustic stimuli. From the fifth to the eighth day the reaction appears in response to a momentary change of illumination. From the ninth to the thirteenth day two stimuli are involved in the organization of the alimentary reaction: a trigger stimulus-a momentary change of illumination, and a directional stimulus-a mobile silhouette of the bird. On the thirteenth to the fifteenth day the alimentary reaction appears only in response to the bird's movement. It is assumed that the successive change of trigger stimuli in one and the same alimentary functional system is determined by a successive involvement of increasingly complicated sensory mechanisms. The time periods of involvement may vary with a change of environmental factors.