Conceptual distinctiveness does not improve visual working memory for objects but aids object-location binding

Visual working memory (VWM) is prone to interference from stored items competing for its limited capacity. These competitive interactions can arise from different sources. For example, one such source is poor item distinctiveness causing a failure to discriminate between items sharing common features. Another source of interference is imperfect binding, a problem of determining which of the remembered features belonged to which object or which item was in which location. In two experiments, we studied how the conceptual distinctiveness of real-world objects (i.e., whether the objects belong to the same or different basic categories) affects VWM for objects and object-location binding. In Experiment 1, we found that distinctiveness did not affect memory for object identities or for locations, but low-distinctive objects were more frequently reported at “swapped” locations that originally went with different objects. In Experiment 2 we found evidence that the effect of distinctiveness on the object-location swaps was due to the use of categorical information for binding. In particular, we found that observers swapped the location of a tested object with another object from the same category more frequently than with any of the objects from another category. This suggests that observers can use some coarse category-location information when objects are conceptually distinct. Taken together, our findings suggest that object distinction and object-location binding act upon different components of VWM.

Memory precision of object-location binding is unimpaired in APOE ε4-carriers with spatial navigation deficits

Research suggests that tests of memory fidelity, feature binding and spatial navigation are promising for early detection of subtle behavioural changes related to Alzheimer’s disease (AD). In the absence of longitudinal data, one way of testing the early detection potential of cognitive tasks is through the comparison of individuals at different genetic risk for AD. Most studies have done so using samples aged 70 years or older. Here, we tested whether memory fidelity of long-term object-location binding may be a sensitive marker even among cognitively healthy individuals in their mid-60s by comparing participants at low and higher risk based on presence of the ε4-allele of the apolipoprotein gene (n=26 ε3ε3 and n=20 ε3ε4 carriers). We used a continuous report paradigm in a visual memory task that required participants to recreate the spatial position of objects in a scene. We employed mixture modelling to estimate the two distinct memory processes that underpin the trial-by-trial variation in localisation errors: retrieval success which indexes the proportion of trials where participants recalled any information about an object’s position and the precision with which participants retrieved this information. Prior work has shown that these memory paradigms that separate retrieval success from precision are capable of detecting subtle differences in mnemonic fidelity even when retrieval success could not. Nonetheless, a Bayesian analysis found good evidence that ε3ε4 carriers did not remember fewer object locations (F(1, 42)=.450, p=.506, BF01=3.02), nor was their precision for the spatial position of objects reduced compared to ε3ε3 carriers (F(1, 42)=.12, p=.726, BF01=3.19). Importantly, ε3ε4-carriers from the same sample have previously been reported to exhibit wayfinding deficits in a spatial navigation task (Coughlan et al. 2019, PNAS, 116(19)). The sensitivity of memory fidelity tasks may therefore not extend to individuals with one ε4-allele in their early to mid-60s. These results provide further support to prior proposals that spatial navigation may be a sensitive marker for the earliest AD-dependent cognitive changes, even before episodic memory. More research in preclinical AD is needed to confirm this hypothesis by direct comparison of memory fidelity and spatial navigation tasks.

Mixed emotions: Competition and context effects of emotional faces in visuospatial working memory

In this study we investigated how differing emotional faces presented in heterogenous displays compete at encoding to influence identity-location binding. Participants were shown four faces and asked to remember their identity and location while their eye-movements were recorded. Two faces carried one emotion while the other two faces carried a different emotion (angry, fear, happy, or sad; emotion was task irrelevant). Participants relocated a single neutrally expressive test face to its original position using a touchscreen. VSWM for emotional faces was modulated by the emotional context. Competition effects were complex and not based on eye-fixation time during the encoding period, stimulus factors (intensity or valence), or on perceptual or response biases. Thus, how emotional faces compete in VSWM appears to rely on more than simple arousal- or valence- biased mechanisms.

Visual spatial attention and spatial working memory do not draw on shared capacity-limited core processes

The extent to which similar capacity limits in visual attention and visual working memory indicate a common shared underlying mechanism is currently still debated. In the spatial domain, the multiple object tracking (MOT) task has been used to assess the relationship between spatial attention and spatial working memory though existing results have been inconclusive. In three dual task experiments, we examined the extent of interference between attention to spatial positions and memory for spatial positions. When the position monitoring task required keeping track of target identities through colour-location binding, we found a moderate detrimental effect of position monitoring on spatial working memory and an ambiguous interaction effect. However, when this task requirement was removed, load increases in neither task were detrimental to the other. The only very moderate interference effect that remained resided in an interaction between load types but was not consistent with shared capacity between tasks—rather it was consistent with content-related crosstalk between spatial representations. Contrary to propositions that spatial attention and spatial working memory may draw on a common shared set of core processes, these findings indicate that for a purely spatial task, perceptual attention and working memory appear to recruit separate core capacity-limited processes.

Evidence for Object-Place binding in pigeons in a sequence-learning procedure

We studied object-location binding in pigeons using a sequence learning procedure. A sequence of four objects was presented, one at a time at one of four locations on a touchscreen. A single peck at the object ended the trial, and food reinforcement was delivered intermittently. In Experiment 1, a between-subjects design was used to present objects, locations, or both in a regular sequence or randomly. Response time costs on nonreinforced probe tests on which object order, location order, or both were disrupted revealed sequence learning effects. Pigeons encoded location order when it was consistent, but not object order when it alone was consistent. When both were consistent, pigeons encoded both, and also showed evidence of object-location binding. In Experiment 2, two groups of pigeons received training on sequences where the same object always appeared at the same location. For some pigeons a consistent sequence was used while for others sequence order was randomized. Only when sequence order was consistent was object-location binding found. These experiments are the first demonstrations of strong and lasting feature binding in pigeons.

Two faces of the attentional blink: Gradual and discrete loss of perceptual awareness

In a series of experiments, the nature of perceptual awareness during the attentional blink was investigated. Previous work has considered the attentional blink as a discrete, all-or-none phenomenon, indicative for access to conscious awareness. Using continuous report measures in combination with mixture modeling, the current outcomes show that, in fact, the attentional blink can be a gradual phenomenon. The nature of the blink depended on whether targets might compete for the same spatial location or not. Without the possibility of spatial overlap, the attentional blink was of a gradual nature, in which representations of blinked targets were impoverished, but nonetheless approached the actual identity of the target that was presented. Conversely, with spatial overlap, the attentional blink was discrete; no partially correct reports could be made about blinked targets. These two different faces of the attentional blink challenge current accounts of awareness and temporal attention, which do not recognize the critical role of feature-location binding in producing discrete task performance, and consequently cannot explain the existence of gradual awareness, including that of targets subject to the attentional blink.