A critical question in the study of human perception is whether information in visual working memory is stored as complete, bound-up objects, or as collections of un-bound visual features. Here I test whether the location of an object is a fundamental feature that is always stored when anything else about the object is, or if it is possible to store other features of an object even with no memory for where it was seen. New experimental paradigms and mathematical models were developed to estimate how many colors, how many locations, and how many color-location conjunctions could be stored. Results across three experiments indicate that about one color is stored with no corresponding memory for where it was seen. This memory is not due to verbal encoding, and does not simply reflect noisy location memory. This freeloating feature greatly constrains theories of how visual information is stored in memory.

This thesis project had the overall aim of investigating older adults (OA) representation of real-world objects through different cognitive paradigms probing visual working memory (vWM) and attention. OAs are known to demonstrate difficulties in these two cognitive domains, however, an under-researched in the aging field is the possible influence of the quality of representations in conjunction with the amount of representations in determining OA’s performances. Moreover, a majority of research in the aging field has utilized geometrical shapes, therefore I was interested to investigate whether the previous findings extend when real-world objects are used. Accordingly, the main questions accordingly probed in this study were 1) whether the content of object representations influence OAs’ performances when vWM and attention are probed, or whether effects are solely due to the amount, and 2) whether age-effects found in previous vWM and attention studies in aging, extend when real-world objects are used. To this aim, Chapter 3 describes two experiments where I manipulated the perceptual and conceptual similarity amongst objects presented to OAs and young adults (YAs) when performing a change detection task taxing vWM. Results indicated both age groups had significantly lower performances when there 3 objects to retain and recall, but no age-related differences in the maintenance and recall of these types of objects. Chapter 4 and Chapter 5 report three experiments addressing the impact of object numerosity and/or nature in OAs’ attention deployment during a visual search task. Results of two experiments in Chapter 4 with manual responses found that OAs’ performance was detrimentally impacted by the amount of object representations, irrespective of the relation amongst the items. Chapter 5 illustrates an eye movement study, aimed at exploring more in detail the visual exploratory behavior of older and young individuals. Overall, OAs were slower and showed a larger tendency to get distracted than YAs, regardless of the perceptual or conceptual target-distractor similarity. Overall, the studies presented in this thesis indicated that aging negatively affects the ability to ignore distracting information. However, little evidence was provided as to whether aging negatively influences the content representation of an object. This result confirms previous research indicating that some, but not all aspects, decline in late adulthood.

Saccadic eye movements, produced by the oculomotor system, are used to bring salient information in line with the high resolution fovea. It has been suggested that visual working memory, the cognitive system that temporarily stores and manipulates visual information (Baddeley & Hitch, 1974), is utilised by the oculomotor system in order to maintain saccade programmes across temporal delays (Belopolsky & Theeuwes, 2011). Saccadic eye movements have been found to deviate away from information stored in visual working memory (Theeuwes and colleagues, 2005, 2006). Saccadic deviation away from presented visual stimuli has been associated with top-down suppression (McSorley, Haggard, & Walker, 2006). This thesis examines the extent to which saccade trajectories are influenced by information held in visual working memory. Through a series of experiments behavioural memory data and saccade trajectory data were explored and evidence for visual working memory-oculomotor interaction was found. Other findings included specific interactions with the oculomotor system for the dorsal and ventral pathways as well as evidence for both bottom-up and top-down processing. Evidence of further oculomotor interaction with manual cognitive mechanisms was also illustrated, suggesting that visual working memory does not uniquely interact with the oculomotor system to preserve saccade programmes. The clinical and theoretical implications of this thesis are explored. It is proposed that the oculomotor system may interact with a variety of sensory systems to inform accurate and efficient visual processing.

An attentional template based on a feature in visual working memory (VWM) can be used to bias attention toward feature-matching objects in the visual field. Attentional guidance based on a single feature is highly efficient and has been well characterized. It is debated, however, whether multiple features can be used to guide attention simultaneously. Some argue that only a single feature in VWM can be elevated to an “active” state and influence perceptual selection. To evaluate whether multiple features can guide attention simultaneously, eye movements were recorded while participants completed both traditional and gaze-contingent visual search tasks. Participants demonstrated guidance by multiple features by switching between relevant colors frequently and without delay. Furthermore, relevant objects of different colors actively competed for saccadic selection. These results provide compelling evidence that multiple attentional templates are able to guide selection simultaneously. Although it was originally proposed that a feature in VWM could also be used to bias attention away from irrelevant items (“template for rejection”), the evidence thus far has been mixed. Some studies report that participants were faster to find a target item after being cued with a distractor feature, suggesting participants were using this feature to avoid matching items, while other studies report a cost and find that participants actually attended to cue-matching items even though they are irrelevant. The current work demonstrates that some evidence in support of feature-guided avoidance can be explained by spatially recoding the cued feature information. Furthermore, when shown a distractor color at the beginning of a trial, participants frequently fixated a matching object early in the trial, but avoided matching objects later in the trial. Other work has suggested that this initial attentional capture by a cue-matching object facilitates later avoidance, but the current data do not support a functional relationship of this nature. In sum, it may not be possible to implement an exclusionary template directly as feature-guided avoidance, but it may be possible to implement indirectly by converting the irrelevant feature information into relevant feature or spatial information.

This dissertation evaluated whether Visual Working Memory (VWM) is a distinct memory system or if it is an activated state of Visual Long Term Memory (VLTM). These two positions suggest different roles for VLTM representations in the performance of VWM. If VWM representations are an activated state of VLTM representations, it seems plausible that strong VLTM representations should facilitate VWM performance. However, if the two representations are actually distinct, it seems less likely that a facilitation interaction between VLTM and VWM representations should be observed. Five experiments were conducted in which participants learned a set of trained stimuli over two days of training. Participant performance with the trained stimuli was compared to performance with novel stimuli on a subsequent VWM change detection task to determine the plausibility of VLTM-VWM interactions. The first and second experiments revealed a LTM facilitation effect that could not be explained by priming, but the third experiment suggested that this facilitation effect was mediated by non-visual representations. The fourth and fifth experiments parceled out the contributions of non-visual memory representations, and failed to demonstrate any evidence of VLTM-VWM performance interactions. These results, in conjunction with other examples from the literature, all converged on the conclusion that VLTM-VWM facilitation interactions are relatively implausible. As such, it was concluded that VWM and VLTM representations are discreet.

The efficiency of human visual information processing is supported by numerous attentional resources. These resources ensure that behaviourally relevant information within visual scenes is selected for detailed processing, while behaviourally irrelevant information is ignored. One of these attentional resources—reflexive visuospatial attention—operates by prioritising locations in visual space in response to the appearance of salient stimuli. The purpose of the present dissertation was to examine how this type of attention contributes to the efficiency of visual processing by asking: How is processing altered for information presented at the location of attention? To develop some initial evidence of the stage of processing affected by reflexive visuospatial attention, Chapters 1 to 6 assessed whether this attentional resource is related to four other stimulus-driven effects that are each associated with a specific stage of visual processing: identity processing, object filtering, visual working memory (VWM), and response generation. Based on the observation that only the stimulus-driven effects on VWM are related to reflexive visuospatial attention (i.e., only those effects were contingent on attentional control settings), a VWM model of reflexive visuospatial attention was proposed in Chapter 7, and tested in Chapters 8 to 11. According to this model, reflexive visuospatial attention alters visual processing by triggering VWM to update. Thus, the effect of reflexive visuospatial attention is to speed the encoding of attended information into VWM. As a result, this information is more likely than unattended information to bias our behaviour, in particular those behaviours that depend on VWM. Further, by biasing VWM, reflexive visuospatial attention can interact with other attentional resources that have also been associated with VWM. In this way, these attentional resources can coordinate in optimising the process of selection, thus, contributing to the efficiency of the human visual system.

The efficiency of human visual information processing is supported by numerous attentional resources. These resources ensure that behaviourally relevant information within visual scenes is selected for detailed processing, while behaviourally irrelevant information is ignored. One of these attentional resources—reflexive visuospatial attention—operates by prioritising locations in visual space in response to the appearance of salient stimuli. The purpose of the present dissertation was to examine how this type of attention contributes to the efficiency of visual processing by asking: How is processing altered for information presented at the location of attention? To develop some initial evidence of the stage of processing affected by reflexive visuospatial attention, Chapters 1 to 6 assessed whether this attentional resource is related to four other stimulus-driven effects that are each associated with a specific stage of visual processing: identity processing, object filtering, visual working memory (VWM), and response generation. Based on the observation that only the stimulus-driven effects on VWM are related to reflexive visuospatial attention (i.e., only those effects were contingent on attentional control settings), a VWM model of reflexive visuospatial attention was proposed in Chapter 7, and tested in Chapters 8 to 11. According to this model, reflexive visuospatial attention alters visual processing by triggering VWM to update. Thus, the effect of reflexive visuospatial attention is to speed the encoding of attended information into VWM. As a result, this information is more likely than unattended information to bias our behaviour, in particular those behaviours that depend on VWM. Further, by biasing VWM, reflexive visuospatial attention can interact with other attentional resources that have also been associated with VWM. In this way, these attentional resources can coordinate in optimising the process of selection, thus, contributing to the efficiency of the human visual system.

Prior research has shown that visual working memory (VWM) performance can be improved via retrospective cues (“retro-cues”) that spatially indicate which item currently being held in working memory will be probed at test. These studies have utilized electroencephalography (EEG) methods to monitor contralateral delay activity (CDA) event related potentials (ERPs) and assert that retro-cues benefit memory by reducing effective memory load. Here, we investigated the potential relationship between CDA amplitude and future long-term memory (LTM) performance. Emerging evidence from ERP and fMRI studies suggest that working memory maintenance can contribute to LTM formation, which suggests that memory systems are not as discrete as some models suggest. We investigated the hypotheses that A) the benefits afforded by the retro-cue in VWM will carry over into LTM, and B) CDA amplitude will be modulated by subsequent LTM performance. Results revealed that retro-cuing improved item accuracy at both VWM and LTM delays, suggesting that the two memory systems are interactive. Due to an insufficient amount of subsequent LTM misses, we were unfortunately too underpowered to detect a CDA depending on long-term memory performance. However, we found that posterior slow-wave potentials during the maintenance period did differ by subsequent LTM performance, which further suggests an interactive systems account of memory. We also sought to investigate what exactly the retro-cue cues. Prior research has focused on memory for items, but no study has questioned if the retro-cue also enhances memory for item location. To this end, the present study investigated the effect of retro-cueing on both item identity and item location. LTM Behavioral results revealed a retro-cue benefit for item accuracy but no benefit for item location, suggesting that the retro-cue selectively cues item identity.

The primary goal of this research was to explore attentional factors contributing to normal balance control and to determine how age-related changes in these factors constrain balance in the aging adult. Though previous research has demonstrated attentional interference between postural control and performance of cognitive tasks in young (YA) and older adults (OA), the mechanisms contributing to interference have not been identified. This study utilized as a cognitive task, a visual working memory task (the change detection task), which identified the short term working memory (or attentional) capacity limits of participants. Participants were asked to perform the cognitive task (determining a change in the color of squares in a first vs. second memory array) either in isolation or with postural tasks of increasing complexity, including quiet sitting (control), quiet stance in isolation, quiet stance (but intermixed with support surface perturbations), and support surface perturbations. YA showed a significant decline in working memory capacity between the control and perturbation condition (p<0.01) but no change in postural performance between single and dual task conditions, as determined by increased steps in response to perturbations (p<0.33). In a second set of experiments, the performance of OA was compared to YA. Results showed that OA had reduced working memory capacity on the change detection task compared to YA even in the control condition (YA: 2.8±0.6 items; OA: 1.8±0.7; p<0.001). OA showed an even greater decline than YA in memory capacity in the dual task condition (p<0.001), along with difficulty regaining balance following perturbations, evidenced by significant increases in up on toes (p<0.05) and stepping strategies (p<0.05). These results suggest that visual working memory (for simple features) and postural control share a common attentional resource that is limited and that postural control is favored over the cognitive task in YA. In OA, attentional capacity was significantly reduced and both postural and cognitive tasks were impaired in the dual task condition, suggesting that with aging even simple cognitive tasks can negatively affect balance under challenging postural conditions.

Most prior investigations of visual working memory (VWM) presented the to-be-remembered items simultaneously in a static configuration (e.g., Luck & Vogel, 1997). However, in everyday situations, such as driving on a busy multilane highway, items (e.g., cars) are presented sequentially and must be retained to support later actions (e.g., knowing if it’s safe to change lanes). In a simultaneous presentation, the relative positions of items are apparent but for sequential presentation, relative positions must be inferred in relation to the background structure (e.g., highway lane markings). To examine sequential encoding in VWM, we developed a novel task in which dots were presented slowly, one at a time, with each dot appearing in one of six boxes (Experiment 1), or in invisible boxes within a visible encompassing outer frame (Experiment 2). Experiment 1 found strong recency effects for judgments of color at the end of the sequence but not for the location of dots. In contrast, without dividing lines, Experiment 2 found strong recency effects for both color and location judgments. These results held true for accuracy, reaction time, and an integrated measure of speed and accuracy. We hypothesize that background structure allows the updating of VWM, slotting each new item into that structure to provide a new configuration that retains both old and new items, whereas in the absence of structure, VWM suffers from severe retroactive interference.