Interference between object-based attention and object-based memory

Research has shown that there are at least two kinds of visual selective attention: location based and object based. In the present study, we sought to determine the locus of spatially invariant object-based selection using a dual-task paradigm. In four experiments, observers performed an attention task (object feature report or visual search) with a concurrent memory task (object memory or spatial memory). Object memory was interfered with more by a concurrent object-based attention task than by a concurrent location-based attention task. However, this interference pattern was reversed for spatial memory, with greater interference by a location-based attention task than by an object-based attention task. These findings suggest that object-based attention and locationbased attention are functionally dissociable and that some forms of object-based selection operate within visual short-term memory.     

Goal-directed access to mental objects in working memory: The role of task-specific feature retrieval

In the present study, we examined the hypothesis of task-specific access to mental objects from verbal working memory. It is currently assumed that a mental object is brought into the focus of attention in working memory by a process of object selection, which provides this object for any upcoming mental operation (Oberauer, 2002). We argue that this view must be extended, since the selection of information for processing is always guided by current intentions and task goals. In our experiments, it was required that two kinds of comparison tasks be executed on digits selected from a set of three digits held in working memory. The tasks differed in regard to the object features the comparison was based on. Access to a new mental object (object switch) took consistently longer on the semantic comparison task than on the recognition task. This difference is not attributable to object selection difficulty and cannot be fully accounted for by task difficulty or differences in rehearsal processes. The results support our assumptions that (1) mental objects are selected for a given specific task and, so, are accessed with their specific task-relevant object features; (2) verbal mental objects outside the focus of attention are usually not maintained at a full feature level but are refreshed phonologically by subvocal rehearsal; and (3) if more than phonological information is required, access to mental objects involves feature retrieval processes in addition to object selection.     

视空工作记忆负载对真实场景搜索绩效的影响

采用视空工作记忆任务和真实场景搜索任务相结合的双任务范式, 结合眼动技术将搜索过程划分为起始阶段、扫描阶段和确认阶段, 探究视空工作记忆负载对真实场景搜索绩效的影响机制, 同时考查试次间搜索目标是否变化、目标模板的具体化程度以及搜索场景画面的视觉混乱度所起的调节作用。结果表明, 视空工作记忆负载会降低真实场景搜索的成绩, 在搜索过程中表现为视空负载条件下扫描阶段持续时间的延长、注视点数目的增加和空间负载条件下确认阶段持续时间的延长, 视空负载对搜索过程的影响与目标模板的具体化程度有关; 空间负载会降低真实场景搜索的效率, 且与搜索画面的视觉混乱度有关, 而客体负载则不会。由此可见, 视空工作记忆负载对真实场景搜索绩效的影响不同, 空间负载对搜索过程的影响比客体负载更长久, 二者均受到目标模板具体化程度的调节; 仅空间负载会降低真实场景的搜索效率, 且受到搜索场景画面视觉混乱度的调节。     

Retro-cue benefits in working memory without sustained focal attention

In working memory (WM) tasks, performance can be boosted by directing attention to one memory object: When a retro-cue in the retention interval indicates which object will be tested, responding is faster and more accurate (the retro-cue benefit). We tested whether the retro-cue benefit in WM depends on sustained attention to the cued object by inserting an attention-demanding interruption task between the retro-cue and the memory test. In the first experiment, the interruption task required participants to shift their visual attention away from the cued representation and to a visual classification task on colors. In the second and third experiments, the interruption task required participants to shift their focal attention within WM: Attention was directed away from the cued representation by probing another representation from the memory array prior to probing the cued object. The retro-cue benefit was not attenuated by shifts of perceptual attention or by shifts of attention within WM. We concluded that sustained attention is not needed to maintain the cued representation in a state of heightened accessibility.     

Brain oscillations during semantic evaluation of speech

Changes in oscillatory brain activity have been related to perceptual and cognitive processes such as selective attention and memory matching. Here we examined brain oscillations, measured with electroencephalography (EEG), during a semantic speech processing task that required both lexically mediated memory matching and selective attention. Participants listened to nouns spoken in male and female voices, and detected an animate target (p = 20%) in a train of inanimate standards or vice versa. For a control task, subjects listened to the same words and detected a target male voice in standards of a female voice or vice versa. The standard trials of the semantic task showed enhanced upper beta (25–30 Hz) and gamma band (GBA, 30–60 Hz) activity compared to the voice task. Upper beta and GBA enhancement was accompanied by a suppression of alpha (8–12 Hz) and lower to mid beta (13–20 Hz) activity mainly localized to posterior electrodes. Enhancement of phase-locked theta activity peaking near 275 ms also occurred over the midline electrodes. Theta, upper beta, and gamma band enhancement may reflect lexically mediated template matching in auditory memory, whereas the alpha and beta suppression likely indicate increased attentional processes and memory demands.     

编码任务对来源记忆的影响:一项事件相关电位研究

本研究采用ERPs技术,探讨编码任务对来源记忆的影响及其神经机制。在学习阶段,被试进行两种编码操作：匹配判断任务和大小判断任务;在测验阶段,让被试进行来源判断任务。行为结果发现：在编码阶段,匹配判断任务比大小判断任务需要更长的时间;在测验阶段,匹配判断任务在“项目旧/背景旧”和“部分旧”条件的正确率显著高于大小判断任务,匹配判断任务在“项目旧/背景旧”条件的反应时显著短于大小判断任务。测验阶段ERPs结果发现：两种编码任务的新旧效应在200~700ms均有较广泛的头皮分布,而在700~1100ms呈前额皮层最大化分布;匹配判断任务的新旧效应比大小判断任务更大,表现在600~700ms的FPz电极以及700~800ms的Pz、P4电极。由此可见,在来源记忆中,编码任务影响来源记忆,主要表现在后部顶区位置;晚期前额皮层新旧效应不受任务难度因素的影响。     

Human frontal midline theta and its synchronization to gamma during a verbal delayed match to sample task

The involvement of oscillatory activity, especially at theta and gamma frequency, in human working memory has been reported frequently. A salient pattern during working memory is electroencephalographic frontal midline theta activity which has been suggested to reflect monitoring functions in order to deal with a task. In general, theta activity has been credited with integrative functions of distributed activity. In the present study, we focused on electroencephalographic power analyses and cross-frequency phase synchronization in order to test whether frontal midline theta activity is linked to more locally generated gamma oscillations during the performance of a verbal delayed match to sample task. The task consisted of two different conditions where subjects either had to reorganize three consonant letters in alphabetical order (manipulation condition) or where they merely had to retain the three consonant letters (retention condition). Results revealed higher frontal midline theta activity for the manipulation of maintained stimulus material compared to pure retention of stimulus material. Interestingly, power differences between conditions were most pronounced during the second half of the delay period. Cross-frequency phase synchronization between frontal midline theta activity and distributed gamma activity, on the other hand, was predominant during the first half of the delay period and was stronger for manipulation compared to retention. We suggest that coupling of frontal midline theta to gamma activity reflects monitoring functions on the temporal segregation of memory items, whereas higher frontal midline theta power in the second half of the delay period might be associated with rehearsal processes. Rehearsal processes in the manipulation condition are likely more pronounced, because rehearsal of a new letter string in a limited time window requires higher mental effort compared to pure retention where rehearsal processes may already start at the beginning of the delay period.     

The impact of object working memory on timing

Nontemporal information processing involving short-term memory requirements disturbs time estimation. Previous studies mostly used letters or digits, which are maintained in working memory by phonological loops. Since verbal and nonverbal information are processed by separate working-memory subsystems, how do nonverbal, object-based memory tasks affect time estimation? We manipulated visual object memory load using the magic cube materials. Participants were divided into three groups, who completed a reaction-time task (control task), a memory-recognition task interposed by an attempt to produce a 2500-ms time interval (active processing), and a memory-recognition task following time interval production (passive retention). The produced time increased with increasing memory-object size under both the active processing and passive retention conditions; mean produced time interval did not significantly differ between the two experimental conditions. By comparing the reaction times and error rates of a relevant task, we excluded any speed–accuracy tradeoff during timing. This result suggests that when the working-memory information to be processed includes objects requiring attention for retention, the production of time intervals is also affected by memory item maintenance.     

Flexible working memory representation of the relationship between an object and its location as revealed by interactions with attention

Working memory (WM) selectively maintains a limited amount of currently relevant information in an active state to influence future perceptual processing, thought, and behavior. The representation of the information held in WM is unknown, particularly the degree of separation between the representation of an object’s identity and its location. The present experiments examined the flexibility of object and location WM representations by measuring reaction times on a visual discrimination task during the delay period of a WM recognition task for object identities, locations, or both. The results demonstrate that during WM delay periods, attention is biased toward information that matches the current contents of WM. Attention is not biased toward information that was present in the encoded memory sample but not relevant for the memory recognition test. This specificity of the interaction between WM and attention applies to both the identity and the location of the remembered stimulus and to the relationship between an object and its location. The results suggest that when this relationship is necessary for task performance, WM represents an object and its identity in an integrated manner. However, if this relationship is not task relevant, the object and location information are represented in WM separately.     

Oscillatory gamma activity in humans and its role in object representation

We experience objects as whole, complete entities irrespective of whether they are perceived by our sensory systems or are recalled from memory. However, it is also known that many of the properties of objects are encoded and processed in different areas of the brain. How then, do coherent representations emerge? One theory suggests that rhythmic synchronization of neural discharges in the gamma band (around 40 Hz) may provide the necessary spatial and temporal links that bind together the processing in different brain areas to build a coherent percept. In this article we propose that this mechanism could also be used more generally for the construction of object representations that are driven by sensory input or internal, top-down processes. The review will focus on the literature on gamma oscillatory activities in humans and will describe the different types of gamma responses and how to analyze them. Converging evidence that suggests that one particular type of gamma activity (induced gamma activity) is observed during the construction of an object representation will be discussed.     

Neural substrates of successful working memory and long-term memory formation in a relational spatial memory task

Working memory (WM) tasks may involve brain activation actually implicated in long-term memory (LTM). In order to disentangle these two memory systems, we employed a combined WM/LTM task, using a spatial relational (object-location) memory paradigm and analyzed which brain areas were associated with successful performance for either task using fMRI. Critically, we corrected for the performance on the respective memory task when analyzing subsequent memory effects. The WM task consisted of a delayed-match-to-sample task assessed in an MRI scanner. Each trial consisted of an indoor or outdoor scene in which the exact configuration of four objects had to be remembered. After a short delay (7–13 s), the scene was presented from a different angle and spatial recognition for two objects was tested. After scanning, participants received an unexpected subsequent recognition memory (LTM) task, where the two previously unprobed objects were tested. Brain activity during encoding, delay phase and probe phase was analyzed based on WM and LTM performance. Results showed that successful WM performance, when corrected for LTM performance, was associated with greater activation in the inferior frontal gyrus and left fusiform gyrus during the early stage of the maintenance phase. A correct decision during the WM probe was accompanied by greater activation in a wide network, including bilateral hippocampus, right superior parietal gyrus and bilateral insula. No voxels exhibited supra-threshold activity during the encoding phase, and we did not find any differential activity for correct versus incorrect trials in the WM task when comparing LTM correct versus LTM incorrect trials.     

A continuous performance task in preschool children: Relations between attention and performance

The continuous performance task is currently used to detect attention disorders in school-age children. However, its use with younger children is problematical, because indices measuring attention indirectly (omissions, commissions, reaction time) may be distorted by difficulties in following instructions: the ability to maintain and manipulate instructions in working memory, and to inhibit inappropriate actions increases with age. In the present research, we adapted such a task for children between 2 years 6months and 5 years 6 months, and recorded visual activity in order to measure directly visual attention and to relate it to performance. Even very young children spend most of the time looking at the screen, but they display poor performances and are unable to re-engage in the task after a gap (2 consecutive omissions). At a medium level (age 3 years 6 months to 4 years) endogenous control of attention increases, children come back to the task, off-task looks shorten and reach the short values observed in older children. After 4 years 6 months no more gaps are observed, the consistency of reaction times shows that a controlled strategy, including shifts from and to the screen, is now adopted. The discussion suggests that only at this upper level do indirect performance indices evaluate attention.     

Cognitive functions of gamma-band activity: memory match and utilization

Oscillatory neural activity in the gamma frequency range (>30Hz) has been shown to accompany a wide variety of cognitive processes. So far, there has been limited success in assigning a unitary basic function to these oscillations, and critics have raised the argument that they could just be an epiphenomenon of neural processing. We propose a new framework that relates gamma oscillations observed in human, as well as in animal, experiments to two underlying processes: the comparison of memory contents with stimulus-related information and the utilization of signals derived from this comparison. This model attempts to explain early gamma-band responses in terms of the match between bottom-up and top-down information. Furthermore, it assumes that late gamma-band activity reflects the readout and utilization of the information resulting from this match.     

Does cross‐frequency phase coupling of oscillatory brain activity contribute to a better understanding of visual working memory?

Nesting of fast rhythmical brain activity (gamma) into slower brain waves (theta) has frequently been suggested as a core mechanism of multi‐item working memory (WM) retention. It provides a better understanding of WM capacity limitations, and, as we discuss in this review article, it can lead to applications for modulating memory capacity. However, could cross‐frequency coupling of brain oscillations also constructively contribute to a better understanding of the neuronal signatures of working memory compatible with theoretical approaches that assume flexible capacity limits? Could a theta‐gamma code also be considered as a neural mechanism of flexible sharing of cognitive resources between memory representations in multi‐item WM? Here, we propose potential variants of theta‐gamma coupling that could explain WM retention beyond a fixed memory capacity limit of a few visual items. Moreover, we suggest how to empirically test these predictions in the future.     

Are age-of-acquisition effects on object naming due simply to differences in object recognition? Comments on Levelt (2002)

Levelt (2002) argued that apparent effects of word frequency and age of acquisition (AoA) reported in recent picture naming studies might actually be confounded effects operating at the level of object recognition, rather than relevant to theories of lexical retrieval. In order to investigate this issue, AoA effects were examined in an object recognition memory task (Experiments 1 and 2) and a word-picture verification task (Experiment 3) and compared with those found in naming tasks using the same pictures. Contrary to Levelt's concerns, the results of the three experiments show that the AoA effect on picture naming has a lexical origin and does not simply result from a possible confound of object identification times.     

Configural and contextual prioritization in object-based attention

When attention is directed to a location within an object, other locations within that object also enjoy an attentional advantage. Recently we demonstrated that this object-based advantage is mediated by increased attentional priority assigned to locations within an already attended object and not to early sensory enhancement due to the "spread" of attention within the attended object (Shomstein & Yantis, 2002). At least two factors might contribute to the assignment of attentional priority, one related to the configuration of objects in a scene and the other related to the probability of target appearance in each location imposed by task contingencies. We investigated the relative contribution of these factors by cuing one end of one of a pair of rectangles; a subsequent target appeared most often in the cued location. We manipulated attentional priority setting by varying (1) the probability that a target would appear in each of two uncued locations and (2) the cue to target stimulus onset asynchrony (SOA). On invalidly cued trials, the target appeared in the high-probability location (defined by an absolute spatial location, e.g., upper right) 83% of the time and in the low-probability location (e.g., lower left) 17% of the time. In both conditions, uncued targets appeared in the cued object half the time and in the uncued object half the time. At short SOAs, the same-object and probability effects were approximately additive. However, at longer SOAs, the same-object effects disappeared, and reaction times depended exclusively on location probability. These results suggest that observers adopt an implicit configural scanning strategy (in which unattended locations within an attended object have high priority) or an implicit contextual scanning strategy (in which objectively high-probability locations have high priority) depending on task contingencies and the amount of time that is available to deploy attention.     

Feature bindings endure without attention: Evidence from an explicit recall task

Are integrated objects the unit of capacity of visual working memory, or is continued attention needed to maintain bindings between independently stored features? In a delayed recall task, participants reported the color and shape of a probed item from a memory array. During the delay, attention was manipulated with an exogenous cue. Recall was elevated at validly cued positions, indicating that the cue affected item memory. On invalid trials, participants most frequently recalled either both features (perfect object memory) or neither of the two features (no object memory); the frequency with which only one feature was recalled was significantly lower than predicted by feature independence as determined in a single-feature recall task. These data do not support the view that features are remembered independently when attention is withdrawn. Instead, integrated objects are stored in visual working memory without need for continued attention.     

无关工作记忆表征的负性情绪信息能否捕获视觉注意?一项眼动研究

研究通过分析视觉搜索任务的首次注视点和行为反应时, 探讨无关工作记忆表征的负性情绪信息对视觉注意选择的影响。实验1发现在反映早期注意选择的首次注视点百分率指标上, 不管工作记忆表征的情绪效价如何, 均出现了显著的注意捕获效应; 实验2发现当采用中性情绪靶子刺激时, 首次注视点百分率指标上仍表现出了稳健的注意捕获效应; 在首次注视点持续时间指标上, 实验1和实验2均发现记忆匹配条件的干扰刺激显著小于控制条件的干扰刺激, 表现出注意的快速脱离; 而在行为反应时指标上, 早期的注意捕获效应消失(实验1), 甚至被反转为注意抑制效应(实验2)。这些结果表明在早期注意选择阶段, 记忆驱动的注意捕获效应不受工作记忆表征情绪效价的影响, 但认知控制会在早期注意捕获之后促使注意快速脱离记忆匹配的干扰刺激, 其作用效果受靶子刺激情绪效价的调节。     

A task-irrelevant stimulus attribute affects perception and short-term memory

Selective attention protects cognition against intrusions of task-irrelevant stimulus attributes. This protective function was tested in coordinated psychophysical and memory experiments. Stimuli were superimposed, horizontally and vertically oriented gratings of varying spatial frequency; only one orientation was task relevant. Experiment 1 demonstrated that a task-irrelevant spatial frequency interfered with visual discrimination of the task-relevant spatial frequency. Experiment 2 adopted a two-item Sternberg task, using stimuli that had been scaled to neutralize interference at the level of vision. Despite being visually neutralized, the task-irrelevant attribute strongly influenced recognition accuracy and associated reaction times (RTs). This effect was sharply tuned, with the task-irrelevant spatial frequency having an impact only when the task-relevant spatial frequencies of the probe and study items were highly similar to one another. Model-based analyses of judgment accuracy and RT distributional properties converged on the point that the irrelevant orientation operates at an early stage in memory processing, not at a later one that supports decision making.     

Strategy-dependent changes in memory: Effects on behavior and brain activity

In the present study, an implicit strategy manipulation was used to explore the contribution of memory strategy to brain activation and behavioral performance. Participants were biased to use either a short-term (maintenance-focused) or long-term (retrieval-focused) memory strategy within a single memory task through manipulation of task context. In comparing directly matched trials across the different task contexts, we observed clear changes in both behavioral performance and brain activity across a network of regions located primarily within lateral and medial frontal cortex. These effects of the memory strategy manipulation suggest that when a retrieval-focused strategy is induced, mnemonic processes are preferentially engaged during the encoding period. In contrast, when a maintenance-focused strategy is induced, mnemonic processes are preferentially engaged during the delay and response periods. Taken together, the results imply that covert cognitive strategies play an important role in modulating brain activation and behavior during memory tasks.