Disruption of delayed memory for a sequence of spatial locations following CA1- or CA3-lesions of the dorsal hippocampus

Axon-sparing neurotoxic lesions of CA1 or CA3 were produced in the dorsal hippocampus to test dissociative lesion effects on spatial working memory for sequential items. Rats were required to remember four different sections sequentially presented on a newly devised maze (i.e., Tulum maze) during a study phase. Each section was cued by a unique object that was specifically associated with each location within the section during the study phase. Following a 15-s delay and during the test phase, rats were required to revisit the location within a section randomly chosen among the previously visited sections in the absence of the cued object. Both CA1 and CA3 lesions similarly disrupted accurate relocation of a previously visited place. However, differential effects of the CA1 and CA3 lesions were observed in serial position curves. CA3-lesions disrupted performance for the first three serial positions, but did not disrupt performance for the last serial position (recency). In contrast, CA1-lesions disrupted performance for all serial positions. The results suggest that temporal separation of spatial memory may depend on the conjoint function of CA1 and CA3 of the hippocampus with a disruption of a spatial pattern completion process following CA3 lesions and a disruption of a temporal pattern separation process following a CA1 lesion.     

Hippocampal CA1 spiking during encoding and retrieval: relation to theta phase

The hippocampal theta rhythm is a prominent oscillation in the field potential observed throughout the hippocampus as a rat investigates stimuli in the environment. A recent computational model [Hasselmo, M. E., Bodelon, C., & Wyble, B. P. (2002a). A proposed function for hippocampal theta rhythm: separate phases of encoding and retrieval enhance reversal of prior learning. Neural Computation, 14, 793-817. Neuromodulation, theta rhythm and rat spatial navigation. Neural Networks, 15, 689-707] suggested that the theta rhythm allows the hippocampal formation to alternate rapidly between conditions that promote memory encoding (strong synaptic input from entorhinal cortex to areas CA3 and CA1) and conditions that promote memory retrieval (strong synaptic input from CA3 to CA1). That model predicted that the preferred theta phase of CA1 spiking should differ for information being encoded versus information being retrieved. In the present study, the spiking activity of CA1 pyramidal cells was recorded while rats performed either an odor-cued delayed nonmatch-to-sample recognition memory test or an object recognition memory task based on the animal's spontaneous preference for novelty. In the test period of both tasks, the preferred theta phase exhibited by CA1 pyramidal cells differed between moments when the rat inspected repeated (match) and non-repeated (nonmatch) items. Also in the present study, additional modeling work extended the previous model to address the mean phase of CA1 spiking associated with stimuli inducing varying levels of retrieval relative to encoding, ranging from novel nonmatch stimuli with no retrieval to highly familiar repeated stimuli with extensive retrieval. The modeling results obtained here demonstrated that the experimentally observed phase differences are consistent with different levels of CA3 synaptic input to CA1 during recognition of repeated items.     

Second-order backward blocking and unovershadowing in human causal learning

De Houwer and Beckers (in press, Experiment 1) recently demonstrated that ratings about the relation between a target cue T2 and an outcome are higher when training involves CT1+ and T1T2+ followed by C+ trials than when training involves CT1+ and T1T2+ followed by C- trials. We replicated this study but now explicitly asked participants to rate the causal status of the cues both before and after the C+ or C- trials. Results showed that causal ratings for T2 were significantly higher after C+ trials than before C+ trials and that T2 received significantly lower ratings after C- trials than before C- trials. The results thus provide the first evidence for higher-order unovershadowing and higher-order backward blocking. In addition, the ratings for T1 revealed that first-order backward blocking (i.e., decrease in ratings for T1 as the result of C+ trials) was stronger than first-order unovershadowing (i.e., increase in ratings for T1 as the result of C- trials).     

Pattern separation, pattern completion, and new neuronal codes within a continuous CA3 map

The hippocampal CA3 subregion is critical for rapidly encoding new memories, which suggests that neuronal computations are implemented in its circuitry that cannot be performed elsewhere in the hippocampus or in the neocortex. Recording studies show that CA3 cells are bound to a large degree to a spatial coordinate system, while CA1 cells can become more independent of a map-based mechanism and allow for a larger degree of arbitrary associations, also in the temporal domain. The mapping of CA3 onto a spatial coordinate system intuitively points to its role in spatial navigation but does not directly suggest how such a mechanism may support memory processing. Although bound to spatial coordinates, the CA3 network can rapidly alter its firing rate in response to novel sensory inputs and is thus not as strictly tied to spatial mapping as grid cells in the medial entorhinal cortex. Such rate coding within an otherwise stable spatial map can immediately incorporate new sensory inputs into the two-dimensional matrix of CA3, where they can be integrated with already stored information about each place. CA3 cell ensembles may thus support the fast acquisition of detailed memories by providing a locally continuous, but globally orthogonal representation, which can rapidly provide a new neuronal index when information is encountered for the first time. This information can be interpreted in CA1 and other downstream cortical areas in the context of less spatially restricted information.     

Visual search by chimpanzees (Pan): assessment of controlling relations.

Three experimentally sophisticated chimpanzees (Pan), Akira, Chloe, and Ai, were trained on visual search performance using a modified multiple-alternative matching-to-sample task in which a sample stimulus was followed by the search display containing one target identical to the sample and several uniform distractors (i.e., negative comparison stimuli were identical to each other). After they acquired this task, they were tested for transfer of visual search performance to trials in which the sample was not followed by the uniform search display (odd-item search). Akira showed positive transfer of visual search performance to odd-item search even when the display size (the number of stimulus items in the search display) was small, whereas Chloe and Ai showed a transfer only when the display size was large. Chloe and Ai used some nonrelational cues such as perceptual isolation of the target among uniform distractors (so-called pop-out). In addition to the odd-item search test, various types of probe trials were presented to clarify the controlling relations in multiple-alternative matching to sample. Akira showed a decrement of accuracy as a function of the display size when the search display was nonuniform (i.e., each "distractor" stimulus was not the same), whereas Chloe and Ai showed perfect performance. Furthermore, when the sample was identical to the uniform distractors in the search display, Chloe and Ai never selected an odd-item target, but Akira selected it when the display size was large. These results indicated that Akira's behavior was controlled mainly by relational cues of target-distractor oddity, whereas an identity relation between the sample and the target strongly controlled the performance of Chloe and Ai.     

Auditory and phonetic processes in speech perception: Evidence from a dichotic study

The distinction between auditory and phonetic processes in speech perception was used in the design and analysis of an experiment. Earlier studies had shown that dichotically presented stop consonants are more often identified correctly when they share place of production (e.g., /ba-pa/) or voicing (e.g., /ba-da/) than when neither feature is shared (e.g., /ba-ta/). The present experiment was intended to determine whether the effect has an auditory or a phonetic basis. Increments in performance due to feature-sharing were compared for synthetic stop-vowel syllables in which formant transitions were the sole cues to place of production under two experimental conditions: (1) when the vowel was the same for both syllables in a dichotic pair, as in our earlier studies, and (2) when the vowels differed. Since the increment in performance due to sharing place was not diminished when vowels differed (i.e., when formant transitions did not coincide), it was concluded that the effect has a phonetic rather than an auditory basis. Right ear advantages were also measured and were found to interact with both place of production and vowel conditions. Taken together, the two sets of results suggest that inhibition of the ipsilateral signal in the perception of dichotically presented speech occurs during phonetic analysis.     

Using stop signals to inhibit chronic dieters' responses toward palatable foods

Palatable foods in the environment can unintentionally trigger reactions to obtain them, which may interfere with dieting attempts. We tested a strategy to facilitate dieting behavior that makes use of behavioral stop signals that should instantly inhibit chronic dieters’ responses toward palatable foods. Participants performed a go/no-go task in which go cues and no-go cues (i.e., the behavioral stop signals) were presented with pictures of palatable foods and control objects. In Study 1, we tested the immediate behavioral effect of presenting stop signals near palatable foods in a reaction time paradigm. In Study 2 we assessed consumption of palatable food that had either consistently been associated with no-go cues, or not. Results show that no-go cues instantly inhibited responses toward palatable foods especially among chronic dieters. Moreover, across a one day period chronic dieters consumed less of a food that had consistently been associated with no-go cues. Stop signals thus appear a promising tool for chronic dieters to control behavior to palatable foods, and we discuss the merits and potential applications of this tool for facilitating dieting behavior.     

Apparent reversals of a rotating mask: A new demonstration of cognition in perception

A mask of a face rotated about its vertical axis of symmetry can appear to oscillate rather than rotate. Do stimulus features (e.g., shape) or cognitive factors (e.g., differential familiarity with convex and concave views of faces) explain this new illusion? In Experiment 1, differential familiarity was varied across stimuli by using familiar and unfamiliar objects rotating at 4 rpm and within stimuli by showing the objects upright and inverted. True motion was seen more with unfamiliar objects than with familiar objects and more with an inverted mask than with an upright mask. The results of Experiment 2, which was done with static views, suggest that the upright and inverted masks present similar structure to the visual system. In Experiment 3, the objects were shown rotating at 8 rpm; the results are similar to those of Experiment 1. These experiments favor a differential familiarity account of this illusory motion. Cognitive constraints on perceived motion and perceived rigidity are discussed.     

Apparent reversals of a rotating mask: a new demonstration of cognition in perception.

A mask of a face rotated about its vertical axis of symmetry can appear to oscillate rather than rotate. Do stimulus features (e.g., shape) or cognitive factors (e.g., differential familiarity with convex and concave views of faces) explain this new illusion? In Experiment 1, differential familiarity was varied across stimuli by using familiar and unfamiliar objects rotating at 4 rpm and within stimuli by showing the objects upright and inverted. True motion was seen more with unfamiliar objects than with familiar objects and more with an inverted mask than with an upright mask. The results of Experiment 2, which was done with static views, suggest that the upright and inverted masks present similar structure to the visual system. In Experiment 3, the objects were shown rotating at 8 rpm; the results are similar to those of Experiment 1. These experiments favor a differential familiarity account of this illusory motion. Cognitive constraints on perceived motion and perceived rigidity are discussed.     

记忆过程中海马CA1区神经元的集群放电特征

观察空间工作记忆过程中海马CA1区神经元群的放电特征。应用多通道神经元集群放电记录技术, 同步观察和记录清醒大鼠在执行延迟选择任务时的行为轨迹以及海马CA1区神经元的放电活动。发现：海马CA1区位置细胞的位置野是在学习过程中逐渐形成并可消退; 部分位置细胞的放电对未来目标定向性行为具有预测作用; 在空间工作记忆过程中, 神经元放电之间的相关性加强, 神经元之间以及神经元与局部场电位之间存在相位编码方式。结果提示海马CA1区神经元参与对空间信息的初级编码和加工, 并为未来行为决策提供有效信息, 而且海马对信息的加工是通过局部神经网络进行, 时间编码可能是海马信息加工的重要方式之一。     

Landmark use by Clark’s nutcrackers (Nucifraga columbiana): influence of disorientation and cue rotation on distance and direction estimates

Many species have been shown to encode multiple sources of information to orient. To examine what kinds of information animals use to locate a goal we manipulated cue rotation, cue availability, and inertial orientation when the food-storing Clark’s nutcracker (Nucifraga columbiana) was searching for a hidden goal in a circular arena. Three groups of birds were used, each with a different goal–landmark distance. As the distance between the goal and the landmark increased, nutcrackers were less accurate in finding the correct direction to the goal than they were at estimating the distance (Experiment 1). To further examine what cues the birds were using to calculate direction, the featural cues within the environment were rotated by 90° and the birds were either oriented when searching (Experiments 2 and 3) or disoriented (Experiment 3). In Experiment 4, all distinctive visual cues were removed (both internal and external to the environment), a novel point of entry was used and the birds were either oriented or disoriented. We found that disorienting the nutcrackers so that they could not use inertial cues did not influence the birds’ total search error. The birds relied heavily but not completely on cues within the environment, as rotating available cues caused them to systematically shift their search behavior. In addition, the birds also relied to some extent on Earth-based cues. These results show the flexible nature of cue use by the Clark’s nutcracker. Our study shows how multiple sources of spatial information may be important for extracting multiple bearings for navigation.     

Establishing global and local correspondence between successive stimuli: the holistic nature of backward alignment

Reflection decisions on alphanumeric characters display systemic effects of disorientation, suggesting that subjects mentally rotate the stimulus to the upright (the uprighting process). However, response time also increases with increasing angular disparity between the current and preceding orientations. This occurs only when the current stimulus is brought into congruence with the preceding one (the backward alignment process). In the present study, we examined the hypothesis that the transformation that occurs in backward alignment in holistic even in tasks in which the uprighting process is likely to be piecemeal. Evidence supporting this hypothesis is presented on the basis of tasks requiring either classification of numbers (Experiments 1 and 3) and words (Experiment 2), or mirror image discrimination on letter pairs (Experiment 4). The results indicated that backward alignment establishes global correspondence between successive stimuli and is indifferent to local correspondence at the level of the constituent elements. The establishment of this global correspondence decreases with the number of elements in the stimulus (Experiment 5), but its effects are still observed for four-letter strings (Experiment 6).     

Why does the effect of short-SOA exogenous cuing on simple RT depend on the number of display locations?

When the stimulus onset asynchrony (SOA) between the cue and target is short (i.e., less than 200 msec) and the number of display locations is small (e.g., only two), exogenous spatial cues produce a benefit in simple response time (RT). However, several recent experiments have found significant costs in these tasks when a large number of display locations is employed (e.g., eight), even at the very short SOAs that usually produce a benefit. The present study explored the dependence of exogenous cuing on the number of display locations and found evidence that both the overall validity of the cues and the specific validity of the cue on the previous trial have strong, additive effects. When a large number of display locations is used, both of these factorswork against a benefit of exogenous cuing on simple RT, reversing the typical finding into a cost. These two effects are suggested to occur within motor and perceptual processes, respectively.     

Does causal knowledge help us be faster and more frugal in our decisions?

One challenge that has to be addressed by the fast and frugal heuristics program is how people manage to select, from the abundance of cues that exist in the environment, those to rely on when making decisions. We hypothesize that causal knowledge helps people target particular cues and estimate their validities. This hypothesis was tested in three experiments. Results show that when causal information about some cues was available (Experiment 1), participants preferred to search for these cues first and to base their decisions on them. When allowed to learn cue validities in addition to causal information (Experiment 2), participants also became more frugal (i.e., they searched fewer of the available cues), made more accurate decisions, and were more precise in estimating cue validities than was a control group that did not receive causal information. These results can be attributed to the causal relation between the cues and the criterion, rather than to greater saliency of the causal cues (Experiment 3). Overall, our results support the hypothesis that causal knowledge aids in the learning of cue validities and is treated as a meta-cue for identifying highly valid cues.     

Dissociations across the dorsal-ventral axis of CA3 and CA1 for encoding and retrieval of contextual and auditory-cued fear

The present study was designed to dissociate the roles of dorsal CA3, dorsal CA1, ventral CA3, and ventral CA1 in contextual and auditory-cued classical fear conditioning. Rats received excitotoxic lesions of dorsal CA3, dorsal CA1, ventral CA3, or ventral CA3 prior to acquisition of classical fear conditioning. Dorsal CA3 and dorsal CA1, but not ventral CA3 or ventral CA1, lesions caused a deficit for the acquisition of contextual fear. Dorsal CA1, ventral CA3, and ventral CA1, but not dorsal CA3, lesions caused deficits for the retrieval/expression of contextual fear when tested either 24 or 48h after encoding. Ventral CA3, but not dorsal CA3, dorsal CA1, or ventral CA1, lesions caused a deficit for retrieval of auditory-cued fear when tested either 24 or 48h after encoding. The data suggest that dorsal CA3 mediates encoding of contextual fear, whereas ventral CA3 mediates retrieval of contextual fear. The data also suggest that dorsal CA1 mediates encoding and retrieval of contextual fear, whereas ventral CA1 mediates only the retrieval of contextual fear.     

Distinct pattern separation related transfer functions in human CA3/dentate and CA1 revealed using high-resolution fMRI and variable mnemonic similarity

Producing and maintaining distinct (orthogonal) neural representations for similar events is critical to avoiding interference in long-term memory. Recently, our laboratory provided the first evidence for separation-like signals in the human CA3/dentate. Here, we extended this by parametrically varying the change in input (similarity) while monitoring CA1 and CA3/dentate for separation and completion-like signals using high-resolution fMRI. In the CA1, activity varied in a graded fashion in response to increases in the change in input. In contrast, the CA3/dentate showed a stepwise transfer function that was highly sensitive to small changes in input.     

Relationship between vection and motion perception in depth

This study examined the effects of cues to motion in depth – namely, stereoscopic (i.e., changing-disparity cues and interocular velocity differences) and changing-size cues on forward and backward vection. We conducted four experiments in which participants viewed expanding or contracting optical flows with the addition of either or both cues. In Experiment 1, participants reported vection by pressing a button whenever they felt it. After each trial, they also rated the magnitude of the vection (from 0 to 100). In Experiments 2 and 3, the participants rated the perceived velocity and motion-in-depth impression of the flows relative to standard stimuli, respectively. In Experiment 4, the participants rated the perceived depth and distance of the display. We observed enhancements in vection, motion-in-depth impression, and perceived depth and distance when either or both types of cues indicated motion-in-depth, as compared to those when the cues did not (Experiments 1, 3, and 4). The perceived velocity changed with cue conditions only for the high velocity condition (Experiment 2). Correlational analyses showed that the vection can be best explained by the motion-in-depth impression. This was partially supported by the multiple regression analyses. These results indicate that the enhancement of vection caused by cues is related to the impression of motion-in-depth rather than the perceived velocity and perceived three-dimensionality.     

Selective deficit of motor imagery as tapped by a left-right decision of visually presented hands

This paper presents the case of MT, a patient suffering from apraxia with left-hemisphere damage who showed a selective deficit in mentally rotating images of hands whereas he was still able to mentally rotate other visual stimuli. The deficit was particularly evident when MT was asked to decide which hand (left or right) was represented in a picture. suggested that in order to carry out this task, participants would mentally rotate a representation of their own body part until it aligns with the stimulus and it does appear that MT's ability to mentally simulate movements is impaired. In contrast, he was able to mentally rotate other forms of bi- and three-dimensional stimuli. Our findings are also consistent with proposal that there are at least two ways in which objects can be mentally rotated, one that recruits processes devoted to motor preparation (e.g., hands), and another that does not.     

Constraints on strategy construction in a speeded discrimination task

In three experiments, subjects reported the identity of a word (above or below) that appeared above or below a fixation point. On some trials, a cue presented 100, 200, 400, 600, 800, or 1,000 msec before the word indicated the relation between position and identity (i.e., whether the dimensions were compatible, e.g., above/above and below/below, or conflicted, e.g., above/below and below/above). On the other trials, the cue was withheld (Experiment 2) or it bore no information about the relation between dimensions (Experiment 1 and 3). In each experiment, the cue reduced reaction time below the level of no-cue or neutral-cue controls, indicating strategic use of the relation between dimensions. Experiments 1 and 2 manipulated the number of potential cues that could occur in a block. A stronger cuing effect was found when one cue could occur (Experiment 2) than when two cues could occur (Experiment 1). Experiment 3 manipulated practice; it revealed that with practice the cuing effect reached asymptote at shorter delays. The asymptote itself did not change. Experiment 4 showed that cue-delay effects were independent of warning interval (warning interval and cue delay confounded in Experiment 1, 2, and 3). The experiments demonstrate construction and utilization of strategies; they show that construction is sensitive to constraints imposed by the subject's goals and abilities and by the structure of the task environment.     

Effects of relevant and irrelevant color singletons on inhibition of return and attentional capture

We tested whether color singletons lead to saccadic and manual inhibition of return (IOR; i.e., slower responses at cued locations) and whether IOR depended on the relevance of the color singletons. The target display was preceded by a nonpredictive cue display. In three experiments, half of the cues were response-relevant, because participants had to perform a discrimination task at the cued location. With the exception of Experiment 2, none of the cue colors matched the target color. We observed saccadic IOR after color singletons, which was greater for slow than for fast responses. Furthermore, when the relevant cue color matched the target color, we observed attentional capture (i.e., faster responses at cued locations) with rapid responses, but IOR with slower responses, which provides evidence for attentional deallocation. When the cue display was completely response-irrelevant in two additional experiments, we did not find evidence for IOR. Instead, we found attentional capture when the cue color matched the target color. Also, attentional capture was greater for rapid responses and with short cue–target intervals. Thus, IOR emerges when cues are relevant and do not match the target color, whereas attentional capture emerges with relevant and irrelevant cues that match the target color.