Despite the concern that has been expressed about potential method biases, and the pervasiveness of research settings with the potential to produce them, there is disagreement about whether they really are a problem for researchers in the behavioral sciences. Therefore, the purpose of this review is to explore the current state of knowledge about method biases. First, we explore the meaning of the terms “method” and “method bias” and then we examine whether method biases influence all measures equally. Next, we review the evidence of the effects that method biases have on individual measures and on the covariation between different constructs. Following this, we evaluate the procedural and statistical remedies that have been used to control method biases and provide recommendations for minimizing method bias.

Sources of Method Bias in Social Science Research and Recommendations on How to Control It

For more than 50 years, psychologists and neuroscientists have recognized the importance of a working memory to coordinate processing when multiple goals are active and to guide behavior with information that is not present in the immediate environment. In recent years, psychological theory and cognitive neuroscience data have converged on the idea that information is encoded into working memory by allocating attention to internal representations, whether semantic long-term memory (e.g., letters, digits, words), sensory, or motoric. Thus, information-based multivariate analyses of human functional MRI data typically find evidence for the temporary representation of stimuli in regions that also process this information in nonworking memory contexts. The prefrontal cortex (PFC), on the other hand, exerts control over behavior by biasing the salience of mnemonic representations and adjudicating among competing, context-dependent rules. The "control of the controller" emerges from a complex interplay between PFC and striatal circuits and ascending dopaminergic neuromodulatory signals.

The Cognitive Neuroscience of Working Memory

Attention is a core property of all perceptual and cognitive operations. Given limited capacity to process competing options, attentional mechanisms select, modulate, and sustain focus on information most relevant for behavior. A significant problem, however, is that attention is so ubiquitous that it is unwieldy to study. We propose a taxonomy based on the types of information that attention operates over—the targets of attention. At the broadest level, the taxonomy distinguishes between external attention and internal attention. External attention refers to the selection and modulation of sensory information. External attention selects locations in space, points in time, or modality-specific input. Such perceptual attention can also select features defined across any of these dimensions, or object representations that integrate over space, time, and modality. Internal attention refers to the selection, modulation, and maintenance of internally generated information, such as task rules, responses, long-term memory, or working memory. Working memory, in particular, lies closest to the intersection between external and internal attention. The taxonomy provides an organizing framework that recasts classic debates, raises new issues, and frames understanding of neural mechanisms.

/pdf/a-taxonomy-of-external-and-internal-attention-3k4coy8dz1.pdf

A taxonomy of external and internal attention.

Working memory is widely considered to be limited in capacity, holding a fixed, small number of items, such as Miller's 'magical number' seven or Cowan's four. It has recently been proposed that working memory might better be conceptualized as a limited resource that is distributed flexibly among all items to be maintained in memory. According to this view, the quality rather than the quantity of working memory representations determines performance. Here we consider behavioral and emerging neural evidence for this proposal.

Changing concepts of working memory.

The Distributed Nature of Working Memory

Working memory (WM) involves maintaining information in an on-line state. One emerging view is that information in WM is maintained via sensory recruitment, such that information is stored via sustained activity in the sensory areas that encode the to-be-remembered information. Using functional magnetic resonance imaging, we observed that key sensory regions such as primary visual cortex (V1) showed little evidence of sustained increases in mean activation during a WM delay period, though such amplitude increases have typically been used to determine whether a region is involved in on-line maintenance. However, a multivoxel pattern analysis of delay-period activity revealed a sustained pattern of activation in V1 that represented only the intentionally stored feature of a multifeature object. Moreover, the pattern of delay activity was qualitatively similar to that observed during the discrimination of sensory stimuli, suggesting that WM representations in V1 are reasonable "copies" of those evoked during pure sensory processing.

/pdf/stimulus-specific-delay-activity-in-human-primary-visual-1heaciwhp5.pdf

Stimulus-Specific Delay Activity in Human Primary Visual Cortex

https://www.cell.com/neuron/pdf/S0896-6273(15)00635-2.pdf

Parietal and Frontal Cortex Encode Stimulus-Specific Mnemonic Representations during Visual Working Memory

Recent studies suggest that visual features are stored in working memory (WM) via sensory recruitment or sustained stimulus-specific patterns of activity in cortical regions that encode memoranda. One important question concerns the spatial extent of sensory recruitment. One possibility is that sensory recruitment is restricted to neurons that are retinotopically mapped to the positions occupied by the remembered items. Alternatively, specific feature values could be represented via a spatially global recruitment of neurons that encode the remembered feature, regardless of the retinotopic position of the remembered stimulus. Here, we evaluated these alternatives by requiring subjects to remember the orientation of a grating presented in the left or right visual field. Functional magnetic resonance imaging and multivoxel pattern analysis were then used to examine feature-specific activations in early visual regions during memory maintenance. Activation patterns that discriminated the remembered feature were found in regions of contralateral visual cortex that corresponded to the retinotopic position of the remembered item, as well as in ipsilateral regions that were not retinotopically mapped to the position of the stored stimulus. These results suggest that visual details are held in WM through a spatially global recruitment of early sensory cortex. This spatially global recruitment may enhance memory precision by facilitating robust population coding of the stored information.

https://www.jneurosci.org/content/jneuro/29/48/15258.full.pdf

Spatially global representations in human primary visual cortex during working memory maintenance.

Restoring Latent Visual Working Memory Representations in Human Cortex

Visual crowding refers to a phenomenon whereby objects that appear in the periphery of the visual field are more difficult to identify when embedded within clutter. Pooling models assert that crowding results from an obligatory averaging or other combination of target and distractor features that occurs prior to awareness. One well-known manifestation of pooling is feature averaging, with which the features of target and nontarget stimuli are combined at an early stage of visual processing. Conversely, substitution models assert that crowding results from binding a target and nearby distractors to incorrect spatial locations. Recent evidence suggests that substitution predominates when target–flanker feature similarity is low, but it is unclear whether averaging or substitution best explains crowding when similarity is high. Here, we examined participants' orientation report errors for targets crowded by similar or dissimilar flankers. In two experiments, we found evidence inconsistent with feature averaging regardless of target–flanker similarity. However, the observed data could be accommodated by a probabilistic substitution model in which participants occasionally “swap” a target for a distractor. Thus, we conclude that—at least for the displays used here—crowding likely results from a probabilistic substitution of targets and distractors, regardless of target–distractor feature similarity.

Edward F. Ester

Papers

Stimulus-Specific Delay Activity in Human Primary Visual Cortex

Parietal and Frontal Cortex Encode Stimulus-Specific Mnemonic Representations during Visual Working Memory

Spatially global representations in human primary visual cortex during working memory maintenance.

Restoring Latent Visual Working Memory Representations in Human Cortex

Substitution and pooling in visual crowding induced by similar and dissimilar distractors