Effects of redundant and orthogonal stimulus dimensions in visual immediate memory search

Visual search and memory search engage extensive overlapping cerebral cortices: an fMRI study

Previous research suggests that traumatic brain injury (TBI) results in impairment of iconic memory abilities.We would like to acknowledge the contribution of Jeffrey D. Vantrease, who wrote the software program for the Iconic Memory procedure and measurement. This raises serious implications for brain injury rehabilitation. Most cognitive rehabilitation programs do not include iconic memory training. Instead it is common for cognitive rehabilitation programs to focus on attention and concentration skills, memory skills, and visual scanning skills.This study compared the iconic memory skills of brain-injury survivors and control subjects who all reached criterion levels of visual scanning skills. This involved previous training for the brain-injury survivors using popular visual scanning programs that allowed them to visually scan with response time and accuracy within normal limits. Control subjects required only minimal training to reach normal limits criteria. This comparison allows for the dissociation of visual scanning skills and iconic memory skills.The results are discussed in terms of their implications for cognitive rehabilitation and the relationship between visual scanning training and iconic memory skills.

<p>Information that is presented visually can be described in terms of its identity and in terms of its position, and a distinction can be drawn between what an item is and where that item is. For example, a letter displayed on a screen has both an identity (its name) and a spatial position; the spatial position can be specified either absolutely (the upper right quadrant) or relatively (beside the "x" and above the "y"). There is an obvious and intimate relationship between the identity component and the position component, and it is this relationship, between the the processing of position information and the processing of identity information, that forms the subject of the present thesis. First, the relevant I literature is reviewed. The relationship between position and identity is examined in the context of two major research areas: iconic memory and short term visual memory. Second, the concept of dimensional separability is considered with reference to the appropriate literature. The purpose is to indicate a theoretical framework within which the issue of concern may be profitably addressed. The key idea to be developed is that position and identity are asymmetrically separable dimensions. A small group of studies that offer tentative support to this conceptualization will be discussed. Third, the results of eight related experiments are reported. These experiments involve the recognition of position and/or identity information in a discrete trials procedure. The eight experiments fall into three separate groups. Experiments 1 to 3 examine the recognition of either position or identity information, with the two types of information presented in relative isolation. Several stimulus factors are manipulated in order to demonstrate differential effects upon the two dimensions. Experiments 4 to 6 examine the effect of the irrelevant dimension upon recognition of the relevant dimension. Experiment 4 uses a logically balanced set of stimuli, so that the irrelevant dimension is either consistent or inconsistent, whereas in Experiments 5 and 6 each dimension is examined in the context of consistent, inconsistent, or neutral information on the irrelevant dimension. Experiments 7 and 8 explore the integration of position and identity information by varying the task requirements. Shared attention conditions are contrasted with selective attention conditions to show the impact of attentional strategy. The thesis concludes with a general discussion of the results, and their accordance with the hypothesis of asymmetric separability.</p>

<p>Information that is presented visually can be described in terms of its identity and in terms of its position, and a distinction can be drawn between what an item is and where that item is. For example, a letter displayed on a screen has both an identity (its name) and a spatial position; the spatial position can be specified either absolutely (the upper right quadrant) or relatively (beside the "x" and above the "y"). There is an obvious and intimate relationship between the identity component and the position component, and it is this relationship, between the the processing of position information and the processing of identity information, that forms the subject of the present thesis. First, the relevant I literature is reviewed. The relationship between position and identity is examined in the context of two major research areas: iconic memory and short term visual memory. Second, the concept of dimensional separability is considered with reference to the appropriate literature. The purpose is to indicate a theoretical framework within which the issue of concern may be profitably addressed. The key idea to be developed is that position and identity are asymmetrically separable dimensions. A small group of studies that offer tentative support to this conceptualization will be discussed. Third, the results of eight related experiments are reported. These experiments involve the recognition of position and/or identity information in a discrete trials procedure. The eight experiments fall into three separate groups. Experiments 1 to 3 examine the recognition of either position or identity information, with the two types of information presented in relative isolation. Several stimulus factors are manipulated in order to demonstrate differential effects upon the two dimensions. Experiments 4 to 6 examine the effect of the irrelevant dimension upon recognition of the relevant dimension. Experiment 4 uses a logically balanced set of stimuli, so that the irrelevant dimension is either consistent or inconsistent, whereas in Experiments 5 and 6 each dimension is examined in the context of consistent, inconsistent, or neutral information on the irrelevant dimension. Experiments 7 and 8 explore the integration of position and identity information by varying the task requirements. Shared attention conditions are contrasted with selective attention conditions to show the impact of attentional strategy. The thesis concludes with a general discussion of the results, and their accordance with the hypothesis of asymmetric separability.</p>

By the late 19th century, tests of adults' shortterm visual memory—how much one retains from a briefly presented display—had acquired a familiar character: An alphanumeric array was presented, removed, and participants were asked to report the items (Wundt, 1912). These ‘whole report’ tests revealed capacities of 3-4 items (Cattell, 1886; Sperling, 1960). However, participants often felt they had seen more items, but forgotten them before report. A crucial innovation was to ask for just a ‘partial report’, cuing participants to sample from their memory (e.g. a high-pitched tone might cue report of the middle of three rows of letters) (Sperling, 1960). If the cue occurs after display offset (a ‘post-cue’) and the sampled subsets are random, then accurate reports mean all the presented items had been stored. This clever methodological change exposed a new—early, high-capacity (∼9 items), and fast-decaying (∼200 ms half-life)—memory system dubbed ‘iconic memory’ (Neisser, 1967). In this sense, then, the study of infants' visual memory is still rooted in the conventions of the 19th century: No one has yet asked infants for a partial report. This leaves a conspicuous gap in our understanding of visual memory development. Research on infants' visual memory has a similarly long history (e.g. Hunter, 1917; Fantz, 1964; Fagan, 1970; for reviews see Nelson, 1995; Rose, Feldman & Jankowski, 2004). And while there has been ample work on infants' short-term memory, for example recency/primacy effects (Olson, 1979; Cornell & Bergstrom, 1983), short-term capacity has been studied only recently (and iconic memory not at all). These studies though have revealed a striking limitation: young infants' short-term memory capacity seems limited to a single object (see Ross-Sheehy, Oakes, & Luck, 2003 for evidence from visual short-term, <300 ms retention interval, memory; Pelphrey et al., 2004 and Kaldy & Leslie, 2005 for evidence from visual working memory). 6-month-olds, then, have sufficiently well-developed visual acuity to distinguish arguably dozens of objects in a single fixation (Teller, 1997), but short-term memory for only one—a curiously inimical constraint unless this object were very well chosen (e.g. by virtue of high salience, task relevance, or cueing). We argue here that iconic memory is the buffer holding the choices.

Suppose you go to the supermarket with a shopping list of 10 items held in memory. Your shopping expedition can be seen as a combination of visual search and memory search. This is known as “hybrid search.” There is a growing interest in understanding how hybrid search tasks are accomplished. We used eye tracking to examine how manipulating the number of possible targets (the memory set size [MSS]) changes how observers (Os) search. We found that dwell time on each distractor increased with MSS, suggesting a memory search was being executed each time a new distractor was fixated. Meanwhile, although the rate of refixation increased with MSS, it was not nearly enough to suggest a strategy that involves repeatedly searching visual space for subgroups of the target set. These data provide a clear demonstration that hybrid search tasks are carried out via a “one visual search, many memory searches” heuristic in which Os examine items in the visual array once with a very low rate of refixations. For each item selected, Os activate a memory search that produces logarithmic response time increases with increased MSS. Furthermore, the percentage of distractors fixated was strongly modulated by the MSS: More items in the MSS led to a higher percentage of fixated distractors. Searching for more potential targets appears to significantly alter how Os approach the task, ultimately resulting in more eye movements and longer response times.

Effects of redundant and irrelevant information on children's seriation ability

Vision and memory are two of the most intensively studied topics in psychology and neuroscience, and the intersection between them — visual memory — is emerging as a fertile ground for research. Certain memory systems appear to specialize in maintaining visually encoded information. Vision provides the primary input to more general memory systems. These more general systems link and integrate visual memory with other perceptual and cognitive processes. As a result, visual perception cannot be understood independently of visual memories, which support the mapping of perceptual input onto existing knowledge structures that guide and constrain perceptual selection. This book provides an account of visual memory systems. The chapters provide both a broad overview of each topic and a summary of the latest research. They also present new perspectives that advance our theoretical understanding of visual memory and suggest directions for future research. After an introductory overview by the editors, chapters address visual sensory memory (iconic memory), visual short-term memory, and the relationship between visual memory and eye movements. Visual long-term memory is then reviewed from several different perspectives, including memory for natural scenes, the relationship between visual memory and object recognition, and associative learning. The final chapters discuss the neural mechanisms of visual memory and neuropsychological deficits in visual memory.

Manipulations of attention dissociate fragile visual short-term memory from visual working memory

In a time-accuracy study, encoding for visual search and memory search was compared in a sample of 23 younger and 26 older adults. Older adults were found to be slower than younger adults in two respects (viz., processing was delayed, and speed-of-processing was lower). There was no reliable age difference in asymptotic performance when analyzed at the level of proportion correct. Age differences in speed-of-processing were larger in visual search than in memory search. The results run counter capacity- or resource accounts of cognitive aging, but they are in line with the framework that predicts larger age differences in visuo-spatial than lexical tasks (Myerson & Hale, 1993).

Four experiments demonstrated that visual search can be decomposed into two components: one consisting of skills shared with memory search and the other consisting of skills not shared with memory search. A training-transfer paradigm was used to test for transfer from memory search to visual search and vice versa. When the same targets and distractors were used in training and transfer, visual search practice completely trained memory search, but memory search practice only partially trained visual search. Learning on both the shared and the private components of visual search benefited more from item-specific training than from nonspecific training. The relationship between the components and some theorized models of visual search are discussed, particularly in terms of prioritization learning.

In hybrid search, observers search for any of several possible targets in a visual display containing distracting items and, perhaps, a target. Wolfe (2012) found that response times (RTs) in such tasks increased linearly with increases in the number of items in the display. However, RT increased linearly with the log of the number of items in the memory set. In earlier work, all items in the memory set were unique instances (e.g., this apple in this pose). Typical real-world tasks involve more broadly defined sets of stimuli (e.g., any "apple" or, perhaps, "fruit"). The present experiments show how sets or categories of targets are handled in joint visual and memory search. In Experiment 1, searching for a digit among letters was not like searching for targets from a 10-item memory set, though searching for targets from an N-item memory set of arbitrary alphanumeric characters was like searching for targets from an N-item memory set of arbitrary objects. In Experiment 2, observers searched for any instance of N sets or categories held in memory. This hybrid search was harder than search for specific objects. However, memory search remained logarithmic. Experiment 3 illustrates the interaction of visual guidance and memory search when a subset of visual stimuli are drawn from a target category. Furthermore, we outline a conceptual model, supported by our results, defining the core components that would be necessary to support such categorical hybrid searches.

In everyday life, we frequently engage in 'hybrid' visual and memory search, where we look for multiple items stored in memory (e.g., a mental shopping list) in our visual environment. Across three experiments, we used event-related potentials to better understand the contributions of visual working memory (VWM) and long-term memory (LTM) during the memory search component of hybrid search. Experiments 1 and 2 demonstrated that the FN400 (an index of LTM recognition) and the CDA (an index of VWM load) increased with memory set size (target load), suggesting that both VWM and LTM are involved in memory search, even when target load exceeds capacity limitations of VWM. In Experiment 3, we used these electrophysiological indices to test how categorical similarity of targets and distractors affects memory search. The CDA and FN400 were modulated by memory set size only if items resembled targets. This suggests that dissimilar distractor items can be rejected before eliciting a memory search. Together, our findings demonstrate the interplay of VWM and LTM processes during memory search for multiple targets.

A crucial function of our goal-directed behavior is to select task-relevant targets among distractor stimuli, some of which may share properties with the target and thus compete for attentional selection. Here, by applying functional magnetic resonance imaging (fMRI) to a visual search task in which a target was embedded in an array of distractors that were homogeneous or heterogeneous along the task-relevant (orientation or form) and/or task-irrelevant (color) dimensions, we demonstrate that for both (orientation) feature search and (form) conjunction search, the fusiform gyrus is involved in processing the task-irrelevant color information, while the bilateral frontal eye fields (FEF), the cortex along the left intraparietal sulcus (IPS), and the left junction of intraparietal and transverse occipital sulci (IPTO) are involved in processing task-relevant distracting information, especially for target-absent trials. Moreover, in conjunction (but not in feature) search, activity in these frontoparietal regions is affected by stimulus heterogeneity along the task-irrelevant dimension: heterogeneity of the task-irrelevant information increases the activity in these regions only when the task-relevant information is homogeneous, not when it is heterogeneous. These findings suggest that differential neural mechanisms are involved in processing task-relevant and task-irrelevant dimensions of the searched-for objects. In addition, they show that the top-down task set plays a dominant role in determining whether or not task-irrelevant information can affect the processing of the task-relevant dimension in the frontoparietal regions.

The role of memory in visual search has become a controversial issue. Most theories of serial visual search support the view that visual search requires memory and a serial scanning mechanism, such as the processes of inhibition of return in serial search (Klein, 1988). However, Horowitz and Wolfe (1998) claimed that serial visual search worked without memory. They compared the search rates in both static and randomly dynamic conditions that prevented parallel accumulation of information of a particular letter and found no significant difference between the two conditions. In the present study, iconic memory was examined in dynamic conditions. Besides, the new object advantage was tested to explain the outcome of Wolfe’s study. In experiment 1 a comparison was made between two conditions: In the restrained dynamic condition, the items moved to positions previously occupied by other items every 110ms. In the static condition, the display items remained in the same location from one frame to the next. In experiment 2 a comparison was made between a restrained dynamic condition and a random condition, in which the items moved to positions not occupied by any item in the last frame. In experiment 3, half of the items moved to new locations and half randomly moved to ones previously occupied. This experiment compared two conditions: the target moving to new locations and the target moving to old locations where items appeared in the last frame. Different groups of students participated in the experiment 1,2 and 3, 10, 14, and 12 students, respectively. In all experiments, the number of letters in the display (set-size) varied between 8, 12, and 16. The slope of the target-present reaction time × set-size function was used to measure the efficiency of display search. Repeated measures ANOVA and linear regression were used to analyze the data. The main results of this study were as follows: first, the efficiency of search under static conditions was significantly higher than that under restrained dynamic conditions; secondly, the efficiency of search under random conditions was also significantly higher than that under restrained dynamic conditions; thirdly, the two conditions in experiment 3 showed no difference. Our results showed that under both random and static conditions visual search required memory, which did not support the visual search model proposed by Horowitz and Wolfe (1998). According to our results, under static conditions, observers might use a static search process and check the items one by one. In addition, under random conditions observers first compare the locations of items in the present frame with the previous locations in the last frame, which were kept in their iconic memory, and then guide attention to focus on new locations and suppress old ones. The findings of our study would help to explain why Wolfe did not observe a difference between static and random conditions and to reveal the role of iconic memory in visual search under random conditions. Finally, our study also indicated that the new object advantage was not significant under random conditions. Generally speaking, iconic memory contributes to the performance of visual search under random conditions by effective guidance of attention.