The locus of color sensation: cortical color loss and the chromatic visual evoked potential.

Color losses of central origin (cerebral achromatopsia and dyschromatopsia) can result from cortical damage and are most commonly associated with stroke. Such cases have the potential to provide useful information regarding the loci of the generation of the percept of color. One available tool to examine this issue is the chromatic visual evoked potential (cVEP). The cVEP has been used successfully to objectively quantify losses in color vision capacity in both congenital and acquired deficiencies of retinal origin but has not yet been applied to cases of color losses of cortical origin. In addition, it is not known with certainty which cortical sites are responsible for the generation of the cVEP waveform components. Here we report psychophysical and electrophysiological examination of a patient with color deficits resulting from a bilateral cerebral infarct in the ventral occipitotemporal region. Although this patient demonstrated pronounced color losses of a general nature, the waveform of the cVEP remains unaffected. Contrast response functions of the cVEP are also normal for this patient. The results suggest that the percept of color arises after the origin of the cVEP and that normal activity in those areas that give rise to the characteristic negative wave of the cVEP are not sufficient to provide for the normal sensation of color.

The effects of divided attention and of stimulus repetition on item-item binding in verbal working memory.

An unresolved issue regarding working memory (WM) processes relates to whether domain-general attentional resources are required to form and store bound representations. Recent evidence suggests that visual WM performance during tasks that require binding of face-scene pairs is disrupted by concurrent divided attention to a greater degree than when needing to remember only faces or scenes (Peterson & Naveh-Benjamin, 2017). These findings contrast with associative long-term memory (LTM) studies, which have found no differential impact of divided attention on associative relative to item memory (Naveh-Benjamin, Guez, & Marom, 2003). In the current study, a verbal WM change detection paradigm, incorporating methods typical of LTM paradigms as well, was leveraged to examine memory for items and item-item bindings, for unrelated word pairs sampled with and without replacement across trials within distinct experimental blocks. In Experiment 1, WM performance was measured under within-domain verbal interference. In Experiment 2, a cross-domain auditory interference task was used to parametrically vary concurrent load. Whereas the results of Experiment 1 revealed that within-domain interference was sufficient to elicit a binding deficit by disrupting verbal rehearsal, in Experiment 2, parametric variation of a cross-domain interference task revealed a divided attention-related binding deficit that increased in magnitude with increased task difficulty. In both experiments, an item-item binding deficit was observed, in comparison with item memory, regardless of whether word pairs were sampled with or without replacement. These findings reveal a dissociable influence of within-domain and cross-domain interference tasks on item-item binding processes in verbal WM. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Further studies on the role of attention and stimulus repetition in item-item binding processes in visual working memory.

A fundamental question for human memory research relates to the role of attention during the binding of distinct components into an integrated representation. A number of important differences exist between the working memory and episodic memory literature in terms of methodological implementation and empirical outcomes. For instance, episodic memory studies indicate that, although divided attention reduces performance, the magnitude of this reduction is similar regardless of whether distinct item components or the associative binding between these components is tested (e.g., Naveh-Benjamin, Guez, & Marom, 2003). In contrast, recent examinations of working memory indicate that reductions in performance under divided attention are larger during tests of item-item binding compared with item tests (Peterson & Naveh-Benjamin, 2017). The current study used methods typical of both episodic and working memory paradigms to further examine the role of attention in item-item binding in visual working memory. Faces and scenes used to create face-scene pairs were either sampled with replacement (i.e., repeated across trials as is typical in working memory experiments) or without replacement (i.e., nonrepeated across trials as is typical in episodic memory experiments) to examine visual working memory performance under parametric variation of concurrent load. Results from Experiment 1 (no load, articulatory suppression) and Experiment 2 (articulatory suppression, backward counting by two) revealed greater reductions in item-item binding relative to single item performance under divided attention regardless of whether item components were repeated or not repeated across trials of each experiment. These results provide further evidence that visual working memory binding requires attention. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Visual working memory deficits in undergraduates with a history of mild traumatic brain injury.

We investigated whether a history of mild traumatic brain injury (mTBI), or concussion, has any effect on visual working memory (WM) performance. In most cases, cognitive performance is thought to return to premorbid levels soon after injury, without further medical intervention. We tested this assumption in undergraduates, among whom a history of mTBI is prevalent. Notably, participants with a history of mTBI performed worse than their colleagues with no such history. Experiment 1 was based on a change detection paradigm in which we manipulated visual WM set size from one to three items, which revealed a significant deficit at set size 3. In Experiment 2 we investigated whether feedback could rescue WM performance in the mTBI group, and found that it failed. In Experiment 3 we manipulated WM maintenance duration (set size 3, 500-1,500 ms) to investigate a maintenance-related deficit. Across all durations, the mTBI group was impaired. In Experiment 4 we tested whether retrieval demands contributed to WM deficits and showed a consistent deficit across recognition and recall probes. In short, even years after an mTBI, undergraduates perform differently on visual WM tasks than their peers with no such history. Given the prevalence of mTBI, these data may benefit other researchers who see high variability in their data. Clearly, further studies will be needed to determine the breadth of the cognitive deficits in those with a history of mTBI and to identify relevant factors that contribute to positive cognitive outcomes.

The role of attention in item-item binding in visual working memory.

An important yet unresolved question regarding visual working memory (VWM) relates to whether or not binding processes within VWM require additional attentional resources compared with processing solely the individual components comprising these bindings. Previous findings indicate that binding of surface features (e.g., colored shapes) within VWM is not demanding of resources beyond what is required for single features. However, it is possible that other types of binding, such as the binding of complex, distinct items (e.g., faces and scenes), in VWM may require additional resources. In 3 experiments, we examined VWM item-item binding performance under no load, articulatory suppression, and backward counting using a modified change detection task. Binding performance declined to a greater extent than single-item performance under higher compared with lower levels of concurrent load. The findings from each of these experiments indicate that processing item-item bindings within VWM requires a greater amount of attentional resources compared with single items. These findings also highlight an important distinction between the role of attention in item-item binding within VWM and previous studies of long-term memory (LTM) where declines in single-item and binding test performance are similar under divided attention. The current findings provide novel evidence that the specific type of binding is an important determining factor regarding whether or not VWM binding processes require attention. (PsycINFO Database Record

The impact of level of education on age-related deficits in associative memory: Behavioral and neuropsychological perspectives.

Older adults have difficulty forming associations and binding distinct item components despite mostly preserved item memory potentially because they rely on more automatic, rather than strategic, processing when attempting to form, store, and retrieve associations from memory. An intriguing possibility is that older adults with greater access to strategic processes (e.g., those with a high level of education) may be less susceptible to age-related associative memory deficits. Two experiments assessed the degree to which a high level of education provides an effective dose of cognitive reserve (CR), potentially preserving associative memory. Standard younger and older adults' item and associative memory performance was compared to older adults who had attained a high level of education (mostly doctoral degrees). In both experiments (Experiment 1: person-action pairs; Experiment 2: unrelated word pairs), consistent evidence was found that older adults, regardless of the level of education, exhibited an age-related associative memory deficit relative to younger adults. Interestingly, neuropsychological assessment of both older adult groups revealed greater frontal lobe, but not enhanced medial temporal lobe, functioning in the highly educated. As such, although the highly educated older adults exhibited greater frontal lobe functioning than the standard older adults, this did not aid in the reduction of the age-related associative memory deficit.

Frontoparietal neurostimulation modulates working memory training benefits and oscillatory synchronization.

There is considerable interest in maintaining working memory (WM) because it is essential to accomplish most cognitive tasks, and it is correlated with fluid intelligence and ecologically valid measures of daily living. Toward this end, WM training protocols aim to improve WM capacity and extend improvements to unpracticed domains, yet success is limited. One emerging approach is to couple WM training with transcranial direct current stimulation (tDCS). This pairing of WM training with tDCS in longitudinal designs promotes behavioral improvement and evidence of transfer of performance gains to untrained WM tasks. However, the mechanism(s) underlying tDCS-linked training benefits remain unclear. Our goal was to gain purchase on this question by recording high-density EEG before and after a weeklong WM training+tDCS study. Participants completed four sessions of frontoparietal tDCS (active anodal or sham) during which they performed a visuospatial WM change detection task. Participants who received active anodal tDCS demonstrated significant improvement on the WM task, unlike those who received sham stimulation. Importantly, this pattern was mirrored by neural correlates in spectral and phase synchrony analyses of the HD-EEG data. Notably, the behavioral interaction was echoed by interactions in frontal-posterior alpha band power, and theta and low alpha oscillations. These findings indicate that one mechanism by which paired tDCS+WM training operates is to enhance cortical efficiency and connectivity in task-relevant networks.

The role of aging in intra-item and item-context binding processes in visual working memory.

Aging is accompanied by declines in both working memory and long-term episodic memory processes. Specifically, important age-related memory deficits are characterized by performance impairments exhibited by older relative to younger adults when binding distinct components into a single integrated representation, despite relatively intact memory for the individual components. While robust patterns of age-related binding deficits are prevalent in studies of long-term episodic memory, observations of such deficits in visual working memory (VWM) may depend on the specific type of binding process being examined. For instance, a number of studies indicate that processes involved in item-context binding of items to occupied spatial locations within visual working memory are impaired in older relative to younger adults. Other findings suggest that intra-item binding of visual surface features (e.g., color, shape), compared to memory for single features, within visual working memory, remains relatively intact. Here, we examined each of these binding processes in younger and older adults under both optimal conditions (i.e., no concurrent load) and concurrent load (e.g., articulatory suppression, backward counting). Experiment 1 revealed an age-related intra-item binding deficit for surface features under no concurrent load but not when articulatory suppression was required. In contrast, in Experiments 2 and 3, we observed an age-related item-context binding deficit regardless of the level of concurrent load. These findings reveal that the influence of concurrent load on distinct binding processes within VWM, potentially those supported by rehearsal, is an important factor mediating the presence or absence of age-related binding deficits within VWM. (PsycINFO Database Record

Contralateral delay activity tracks the influence of Gestalt grouping principles on active visual working memory representations.

Recent studies have demonstrated that factors influencing perception, such as Gestalt grouping cues, can influence the storage of information in visual working memory (VWM). In some cases, stationary cues, such as stimulus similarity, lead to superior VWM performance. However, the neural correlates underlying these benefits to VWM performance remain unclear. One neural index, the contralateral delay activity (CDA), is an event-related potential that shows increased amplitude according to the number of items held in VWM and asymptotes at an individual's VWM capacity limit. Here, we applied the CDA to determine whether previously reported behavioral benefits supplied by similarity, proximity, and uniform connectedness were reflected as a neural savings such that the CDA amplitude was reduced when these cues were present. We implemented VWM change-detection tasks with arrays including similarity and proximity (Experiment 1); uniform connectedness (Experiments 2a and 2b); and similarity/proximity and uniform connectedness (Experiment 3). The results indicated that when there was a behavioral benefit to VWM, this was echoed by a reduction in CDA amplitude, which suggests more efficient processing. However, not all perceptual grouping cues provided a VWM benefit in the same measure (e.g., accuracy) or of the same magnitude. We also found unexpected interactions between cues. We observed a mixed bag of effects, suggesting that these powerful perceptual grouping benefits are not as predictable in VWM. The current findings indicate that when grouping cues produce behavioral benefits, there is a parallel reduction in the neural resources required to maintain grouped items within VWM.

Hits and misses: leveraging tDCS to advance cognitive research.

The popularity of non-invasive brain stimulation techniques in basic, commercial, and applied settings grew tremendously over the last decade. Here, we focus on one popular neurostimulation method: transcranial direct current stimulation (tDCS). Many assumptions regarding the outcomes of tDCS are based on the results of stimulating motor cortex. For instance, the primary motor cortex is predictably suppressed by cathodal tDCS or made more excitable by anodal tDCS. However, wide-ranging studies testing cognition provide more complex and sometimes paradoxical results that challenge this heuristic. Here, we first summarize successful efforts in applying tDCS to cognitive questions, with a focus on working memory (WM). These recent findings indicate that tDCS can result in cognitive task improvement or impairment regardless of stimulation site or direction of current flow. We then report WM and response inhibition studies that failed to replicate and/or extend previously reported effects. From these opposing outcomes, we present a series of factors to consider that are intended to facilitate future use of tDCS when applied to cognitive questions. In short, common pitfalls include testing too few participants, using insufficiently challenging tasks, using heterogeneous participant populations, and including poorly motivated participants. Furthermore, the poorly understood underlying mechanism for long-lasting tDCS effects make it likely that other important factors predict responses. In conclusion, we argue that although tDCS can be used experimentally to understand brain function its greatest potential may be in applied or translational research.

The steady-state visual evoked potential reveals neural correlates of the items encoded into visual working memory.

Visual working memory (VWM) capacity limitations are estimated to be ~4 items. Yet, it remains unclear why certain items from a given memory array may be successfully retrieved from VWM and others are lost. Existing measures of the neural correlates of VWM cannot address this question because they measure the aggregate processing of the entire stimulus array rather than neural signatures of individual items. Moreover, this cumulative processing is usually measured during the delay period, thereby reflecting the allocation of neural resources during VWM maintenance. Here, we use the steady-state visual evoked potential (SSVEP) to identify the neural correlates of individual stimuli at VWM encoding and test two distinct hypotheses: the focused-resource hypothesis and the diffuse-resource hypothesis, for how the allocation of neural resources during VWM encoding may contribute to VWM capacity limitations. First, we found that SSVEP amplitudes were larger for stimuli that were later remembered than for items that were subsequently forgotten. Second, this pattern generalized so that the SSVEP amplitudes were also larger for the unprobed stimuli in correct compared to incorrect trials. These data are consistent with the diffuse-resource view in which attentional resources are broadly allocated across the whole stimulus array. These results illustrate the important role encoding mechanisms play in limiting the capacity of VWM.

The Gestalt principle of similarity benefits visual working memory.

Visual working memory (VWM) is essential for many cognitive processes, yet it is notably limited in capacity. Visual perception processing is facilitated by Gestalt principles of grouping, such as connectedness, similarity, and proximity. This introduces the question, do these perceptual benefits extend to VWM? If so, can this be an approach to enhance VWM function by optimizing the processing of information? Previous findings have demonstrated that several Gestalt principles (connectedness, common region, and spatial proximity) do facilitate VWM performance in change detection tasks (Jiang, Olson, & Chun, 2000; Woodman, Vecera, & Luck, 2003; Xu, 2002, 2006; Xu & Chun, 2007). However, one prevalent Gestalt principle, similarity, has not been examined with regard to facilitating VWM. Here, we investigated whether grouping by similarity benefits VWM. Experiment 1 established the basic finding that VWM performance could benefit from grouping. Experiment 2 replicated and extended this finding by showing that similarity was only effective when the similar stimuli were proximal. In short, the VWM performance benefit derived from similarity was constrained by spatial proximity, such that similar items need to be near each other. Thus, the Gestalt principle of similarity benefits visual perception, but it can provide benefits to VWM as well.

Differential frontal involvement in shifts of internal and perceptual attention.

BACKGROUND: Perceptual attention enhances the processing of items in the environment, whereas internal attention enhances processing of items encoded in visual working memory. In perceptual and internal attention cueing paradigms, cues indicate the to-be-probed item before (pre-cueing) or after (retro-cueing) the memory display, respectively. Pre- and retro-cues confer similar behavioral accuracy benefits (pre-: 14-19%, retro-: 11-17%) and neuroimaging data show that they activate overlapping frontoparietal networks. Yet reports of behavioral and neuroimaging differences suggest that pre- and retro-cueing differentially recruit frontal and parietal cortices (Lepsien and Nobre, 2006). OBJECTIVE/HYPOTHESIS: This study examined whether perceptual and internal attention are equally disrupted by neurostimulation to frontal and parietal cortices. We hypothesized that neurostimulation applied to frontal cortex would disrupt internal attention to a greater extent than perceptual attention. METHODS: Cathodal transcranial direct current stimulation (tDCS) was applied to frontal or parietal cortices. After stimulation, participants completed a change detection task coupled with either pre- or retro-cues. RESULTS: Cathodal tDCS across site (frontal, parietal) hindered performance. However, frontal tDCS had a greater negative impact on the retro-cued trials demonstrating greater frontal involvement during shifts of internal attention. CONCLUSIONS: These results complement the neuroimaging data and provide further evidence suggesting that perceptual and internal attention are not identical processes. We conclude that although internal and perceptual attention are mediated by similar frontoparietal networks, the weight of contribution of these structures differs, with internal attention relying more heavily on the frontal cortex.

The 'bookshelf illusion'--a real-world Zöllner-type illusion?

We discovered an interesting perceptual distortion in our office where an upright lamp in front of a bookshelf was noticeably curved to form several subtle S-shaped bends. We realized that the books in the bookshelf fell in a particular manner, leaning in alternative directions, which caused the straight lamp to appear bent, creating what may be a real-world example of the Zöllner illusion. Evidence for the production of the illusion diagrammatically and an explanation for the effect are provided.

PsychoPro 2.0: using multidimensional scaling to examine the perceptual categorization of race.

Recently, researchers examining cognitive mechanisms involved in the detection of racial markers have been using psychophysics to examine perceptual thresholds delineating race using a program called PsychoPro (MacLin, MacLin, Peterson, Chowdhry, & Joshi, 2009). PsychoPro allows researchers to collect data using facial stimuli morphed along a racial continuum with psychophysical methodology. PsychoPro 2.0 was updated so researchers could collect paired-comparison data that can then be analyzed using multidimensional scaling (MDS). MDS allows researchers to examine the perceptions of racial boundaries along perceptual dimensions not bounded by the stimulus continuum, by having the observer make paired comparisons to racial stimuli based on their perceived similarity. Results indicate that ratings were made on the basis of at least six different racial dimensions that suggest the emergence of a third race not represented by the original morph starting images. Details of the software, the new paired-comparison feature and its relevance in psychophysical studies in general and racial categorization in particular are presented.