Spatial working memory capacity predicts bias in estimates of location

Corvids optimize working memory by categorizing continuous stimuli

Working memory (WM) is a crucial element of the higher cognition of primates and corvid songbirds. Despite its importance, WM has a severely limited capacity and is vulnerable to noise. In primates, attractor dynamics mitigate the effect of noise by discretizing continuous information. Yet, it remains unclear whether similar dynamics are seen in avian brains. Here, we show jackdaws (Corvus monedula) have similar behavioral biases as humans; memories are less precise and more biased as memory demands increase. Model-based analysis reveal discrete attractors are evenly spread across the stimulus space. Altogether, our comparative approach suggests attractor dynamics in primates and corvids mitigate the effect of noise by systematically drifting towards specific attractors. By demonstrating this effect in an evolutionary distant species, our results strengthen attractor dynamics as general, adaptive biological principle to efficiently use WM.

Attractor dynamics with activity-dependent plasticity capture human working memory across time scales

Most cognitive functions require the brain to maintain immediately preceding stimuli in working memory. Here, using a human working memory task with multiple delays, we test the hypothesis that working memories are stored in a discrete set of stable neuronal activity configurations called attractors. We show that while discrete attractor dynamics can approximate working memory on a single time scale, they fail to generalize across multiple timescales. This failure occurs because at longer delay intervals the responses contain more information about the stimuli than can be stored in a discrete attractor model. We present a modeling approach that combines discrete attractor dynamics with activity-dependent plasticity. This model successfully generalizes across all timescales and correctly predicts intertrial interactions. Thus, our findings suggest that discrete attractor dynamics are insufficient to model working memory and that activity-dependent plasticity improves durability of information storage in attractor systems.

Individual differences in spatial working memory strategies differentially reflected in the engagement of control and default brain networks

Spatial locations can be encoded and maintained in working memory using high-precision, fine-grained representations that are cognitively demanding, or coarse and less demanding categorical representations. In this study, we employed an individual differences approach to identify brain activity correlates of the use of fine-grained and categorical representations in spatial working memory. We combined data from six fMRI studies, resulting in a sample of 153 (77 women, 25 ± 6 years) healthy participants performing a spatial working memory task. Our results showed that individual differences in the use of spatial representations in working memory were associated with distinct patterns of brain activation, with fine-grained representations requiring greater engagement of attentional and control brain systems, while categorical representations were associated with decreased inhibition of the default network. These findings may indicate a greater need for ongoing maintenance and protection against interference for fine-grained compared to categorical representations.

Familiarity enhances mnemonic precision but impairs mnemonic accuracy in visual working memory

Prior stimulus familiarity has a variety of effects on visual working memory representations and processes. However, it is still unclear how familiarity interacts with the veridical correspondence between mnemonic representation and external stimuli. Here, we examined the effect of familiarity on two aspects of mnemonic correspondence, precision and accuracy, in visual working memory. Specifically, we used a hierarchical Bayesian method to model task performance in a change detection task with celebrity lookalikes (morphed faces between celebrities and noncelebrities with various ratios) as the memory stimuli. We found that familiarity improves memory precision by sharpening mnemonic representation but impairs memory accuracy by biasing mnemonic representation toward familiar faces (i.e., celebrity faces). These findings provide an integrated account of the puzzling celebrity sighting phenomena with the dissociable effects on mnemonic imprecision and bias and further highlight the importance of assessing these two aspects of memory correspondence in future research.

Bounded rational decision-making models suggest capacity-limited concurrent motor planning in human posterior parietal and frontal cortex

While traditional theories of sensorimotor processing have often assumed a serial decision-making pipeline, more recent approaches have suggested that multiple actions may be planned concurrently and vie for execution. Evidence for the latter almost exclusively stems from electrophysiological studies in posterior parietal and premotor cortex of monkeys. Here we study concurrent prospective motor planning in humans by recording functional magnetic resonance imaging (fMRI) during a delayed response task engaging movement sequences towards multiple potential targets. We find that also in human posterior parietal and premotor cortex delay activity modulates both with sequence complexity and the number of potential targets. We tested the hypothesis that this modulation is best explained by concurrent prospective planning as opposed to the mere maintenance of potential targets in memory. We devise a bounded rationality model with information constraints that optimally assigns information resources for planning and memory for this task and determine predicted information profiles according to the two hypotheses. When regressing delay activity on these model predictions, we find that the concurrent prospective planning strategy provides a significantly better explanation of the fMRI-signal modulations. Moreover, we find that concurrent prospective planning is more costly and thus limited for most subjects, as expressed by the best fitting information capacities. We conclude that bounded rational decision-making models allow relating both behavior and neural representations to utilitarian task descriptions based on bounded optimal information-processing assumptions.

When the future is uncertain, it can be beneficial to concurrently plan several action possibilities in advance. Electrophysiological research found evidence in monkeys that brain regions in posterior parietal and promotor cortex are indeed capable of planning several actions in parallel. We now used fMRI to study brain activity in these brain regions in humans. For our analyses we applied bounded rationality models that optimally assign information resources to fMRI activity in a complex motor planning task. We find that theoretical information costs of concurrent prospective planning explained fMRI activity profiles significantly better than assuming alternative memory-based strategies. Moreover, exploiting the model allowed us to quantify the individual capacity limit for concurrent planning and to relate these individual limits to both subjects’ behavior and to their neural representations of planning.

The role of memory and perspective shifts in systematic biases during object location estimation

In the current study, we investigated whether the introduction of perspective shifts in a spatial memory task results in systematic biases in object location estimations. To do so, we asked participants to first encode the position of an object in a virtual room and then to report its position from memory or perception following a perspective shift. Overall, our results showed that participants made systematic errors in estimating object positions in the same direction as the perspective shift. Notably, this bias was present in both memory and perception conditions. We propose that the observed systematic bias was driven by difficulties in understanding the perspective shifts that led participants to use an egocentric representation of object positions as an anchor when estimating the object location following a perspective shift.

Errors in visuospatial working memory across space and time

Visuospatial working memory (VSWM) involves cortical regions along the dorsal visual pathway, which are topographically organized with respect to the visual space. However, it remains unclear how such functional organization may constrain VSWM behavior across space and time. Here, we systematically mapped VSWM performance across the 2-dimensional (2D) space in various retention intervals in human subjects using the memory-guided and visually guided saccade tasks in two experiments. Relative to visually guided saccades, memory-guided saccades showed significant increases in unsystematic errors, or response variability, with increasing target eccentricity (3°–13° of visual angle). Unsystematic errors also increased with increasing delay (1.5–3 s, Experiment 1; 0.5–5 s, Experiment 2), while there was little or no interaction between delay and eccentricity. Continuous bump attractor modeling suggested neurophysiological and functional organization factors in the increasing unsystematic errors in VSWM across space and time. These findings indicate that: (1) VSWM representation may be limited by the functional topology of the visual pathway for the 2D space; (2) Unsystematic errors may reflect accumulated noise from memory maintenance while systematic errors may originate from non-mnemonic processes such as noisy sensorimotor transformation; (3) There may be independent mechanisms supporting the spatial and temporal processing of VSWM.

Sensory- and memory-related drivers for altered ventriloquism effects and aftereffects in older adults

The manner in which humans exploit multisensory information for subsequent decisions changes with age. Multiple causes for such age-effects are being discussed, including a reduced precision in peripheral sensory representations, changes in cognitive inference about causal relations between sensory cues, and a decline in memory contributing to altered sequential patterns of multisensory behaviour. To dissociate these putative contributions, we investigated how healthy young and older adults integrate audio-visual spatial information within trials (the ventriloquism effect) and between trials (the ventriloquism aftereffect). With both a model-free and (Bayesian) model-based analyses we found that both biases differed between groups. Our results attribute the age-change in the ventriloquism bias to a decline in spatial hearing rather than a change in cognitive processes. This decline in peripheral function, combined with a more prominent influence from preceding responses rather than preceding stimuli in the elderly, can also explain the observed age-effect in the ventriloquism aftereffect. Our results suggest a transition from a sensory-to a behavior-driven influence of past multisensory experience on perceptual decisions with age, due to reduced sensory precision and change in memory capacity.

Robust spatial ventriloquism effect and trial-by-trial aftereffect under memory interference

Our brain adapts to discrepancies in the sensory inputs. One example is provided by the ventriloquism effect, experienced when the sight and sound of an object are displaced. Here the discrepant multisensory stimuli not only result in a biased localization of the sound, but also recalibrate the perception of subsequent unisensory acoustic information in the so-called ventriloquism aftereffect. This aftereffect has been linked to memory-related processes based on its parallels to general sequential effects in perceptual decision making experiments and insights obtained in neuroimaging studies. For example, we have recently implied memory-related medial parietal regions in the trial-by-trial ventriloquism aftereffect. Here, we tested the hypothesis that the trial-by-trial (or immediate) ventriloquism aftereffect is indeed susceptible to manipulations interfering with working memory. Across three experiments we systematically manipulated the temporal delays between stimuli and response for either the ventriloquism or the aftereffect trials, or added a sensory-motor masking trial in between. Our data reveal no significant impact of either of these manipulations on the aftereffect, suggesting that the recalibration reflected by the trial-by-trial ventriloquism aftereffect is surprisingly resilient to manipulations interfering with memory-related processes.

Reply to Duffy and Smith's (2018) reexamination

Duffy, Huttenlocher, Hedges, and Crawford (2010, Psychonomic Bulletin & Review, 17[2], 224-230) examined whether the well-established central tendency bias in people's reproductions of stimuli reflects bias toward the mean of an entire presented distribution or bias toward only recently seen stimuli. They reported evidence that responses were biased toward the long-run mean and found no evidence that they were biased toward the most recent stimuli. Duffy and Smith (2018) reexamine the data using a different analytical strategy and argue that estimates are biased by recent stimuli rather than toward the long-run mean. I argue that this reanalysis misses a true effect of the running mean and that the data are (mostly) consistent with the claims in the original work. I suggest that these results, and many other null results presented by Duffy and Smith, do not have major theoretical significance for the category adjustment model and similar Bayesian models. (Code and data available: https://osf.io/tkqvn .).

Bayesian average or truncation at boundaries? The mechanisms underlying categorical bias in spatial memory

Spatial memory is often biased by various factors, such as the region a target belongs to, which can be defined based on physical, perceptual, or implicit boundaries. In the typical dot-localization task first introduced by Huttenlocher, Hedges, and Duncan (Psychological Review 98: 352-376, 1991), individuals normally divide the task space into four quadrants delineated at the Cartesian axes (forming "default categories") and show systematic bias in target localization toward the center of the category. At least two mechanisms have been proposed to account for these categorical biases, namely (a) weighted-average of a metric representation and the category prototype representation and (b) truncation of an un-biased metric representation at the category boundary. Both models can account for these findings and cannot be differentiated by existing research methods. Using a new distribution analysis, the current study sought to differentiate between these two models. Participants viewed a dot inside a circle and recalled its location after a delay either with the same blank circle (i.e., the standard dot-in-circle paradigm) or when an alternative V-shaped category boundary was visually presented at retrieval. The data from three experiments showed symmetrical distribution of the errors that shifted toward the category center when people primarily used the default category, supporting the weighted-average model. In contrast, when people primarily used the alternative category, the errors showed a highly skewed distribution, more consistent with the truncation model. Overall, these results provided the first experimental evidence for both mechanisms separately.

Bias and ignorance in demographic perception

When it comes to knowledge of demographic facts, misinformation appears to be the norm. Americans massively overestimate the proportions of their fellow citizens who are immigrants, Muslim, LGBTQ, and Latino, but underestimate those who are White or Christian. Previous explanations of these estimation errors have invoked topic-specific mechanisms such as xenophobia or media bias. We reconsidered this pattern of errors in the light of more than 30 years of research on the psychological processes involved in proportion estimation and decision-making under uncertainty. In two publicly available datasets featuring demographic estimates from 14 countries, we found that proportion estimates of national demographics correspond closely to what is found in laboratory studies of quantitative estimates more generally. Biases in demographic estimation, therefore, are part of a very general pattern of human psychology-independent of the particular topic or demographic under consideration-that explains most of the error in estimates of the size of politically salient populations. By situating demographic estimates within a broader understanding of general quantity estimation, these results demand reevaluation of both topic-specific misinformation about demographic facts and topic-specific explanations of demographic ignorance, such as media bias and xenophobia.

The unreliability of egocentric bias across self-other and memory-belief distinctions in the Sandbox Task

Humans are often considered egocentric creatures, particularly (and ironically) when we are supposed to take another person's perspective over our own (i.e. when we use our theory of mind). We investigated the underlying causes of this phenomenon. We gave young adult participants a false belief task (Sandbox Task) in which objects were first hidden at one location by a protagonist and then moved to a second location within the same space but in the protagonist's absence. Participants were asked to indicate either where the protagonist remembered the item to be (reasoning about another's memory), believed it to be (reasoning about another's false belief), or where the protagonist would look for it (action prediction of another based on false belief). The distance away from Location A (the original one) towards Location B (the new location) was our measure of egocentric bias. We found no evidence that egocentric bias varied according to reasoning type, and no evidence that participants actually were more biased when reasoning about another person than when simply recalling the first location from memory. We conclude that the Sandbox Task paradigm may not be sensitive enough to draw out consistent effects related to mental state reasoning in young adults.

Short-term memory for spatial, sequential and duration information

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Analog report methods provide novel insights on STM for space and time.

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Space and time may be used to bind features in STM.

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The hippocampus is involved in object-location binding in STM.

Space and time appear to play key roles in the way that information is organized in short-term memory (STM). Some argue that they are crucial contexts within which other stored features are embedded, allowing binding of information that belongs together within STM. Here we review recent behavioral, neurophysiological and imaging studies that have sought to investigate the nature of spatial, sequential and duration representations in STM, and how these might break down in disease. Findings from these studies point to an important role of the hippocampus and other medial temporal lobe structures in aspects of STM, challenging conventional accounts of involvement of these regions in only long-term memory.