Learning & Memory

Memory faces a fundamental challenge. It has to become flexible enough to be accessed by novel cues without losing the specific information that defines each individual episode. Whether memory transformation solves this problem by sacrificing details or by adaptively expanding retrieval while preserving them is unclear. We tested this by manipulating the match between a memory and its retrieval cue. Participants retrieved object associations after 6, 24 and 48 hours using either the original encoded image or novel exemplars that were more typical or more distinctive of the same object category. Retrieval initially benefited from the originally encoded image, but this advantage was reduced across delay. By 48 hours, a never-seen, more typical exemplar triggered retrieval as effectively as the original one, while the same convergence was not evident for less-typical exemplars. Crucially, such cue expansion was not accompanied by a loss of perceptual specificity. Participants retained access to the originally encoded exemplar across delays, while errors increasingly favoured more typical alternatives. At the item level, stronger episodic memories predicted better access to perceptual detail, but did not predict the tendency of errors for category-like information, which instead increased with delay. This dissociation suggests that memory generalisation and the continued accessibility of visual detail reflect partly separable transformations rather than opposite ends of a single continuum.

Extensive work has established that exposure to a single acute stressor can have profound impacts on future reactivity to new stressors, including enhanced acquisition of new fear. The impact of stressor type on development of stress sensitization, however, remains unclear. We investigated whether fundamentally different acute stressors (shock, social defeat, or restraint stress) differ in ability to sensitize acquisition of a new, contextually distinct fear memory in adult male mice two weeks following stress exposure. Stressor subtype differentially sensitized new fear learning; specifically, shock and social defeat - but not restraint stress - led to enhanced recall of a new shock-paired fear memory. We also compared how stressor subtypes differentially engage the brain-periphery interactions that regulate stress responsivity. Notably, restraint stress, which did not lead to fear sensitization to foot shock, drove similar or even greater corticosterone release than other stressors, suggesting that the neuroendocrine response to the original stressor is dissociable from development of a behavioural fear sensitization response. Using the immediate-early gene FOS as a marker of neural activity, all conditions - including the context-only control condition - activated a similar number of neurons in the basolateral amygdala. In contrast, only stressful conditions activated the paraventricular nucleus of the hypothalamus, and restraint stress selectively spared activation of the dorsal hippocampus. These data collectively suggest that future responses to stress depend critically on the identity of previously experienced stressors, rather than simply on prior exposure to stress, establishing a powerful comparative model for investigating the specific mechanisms underlying stress-enhanced fear learning.

Hippocampal place cells encode spatial information within a theta-organized temporal framework paced by the medial septum (MS). Lesions or inactivation of the MS impair spatial learning and disrupt hippocampal theta rhythmicity, long-term potentiation, and plasticity-related gene expression, while often sparing spatially selective firing of CA1 neurons (but not CA3 neurons). Although many rodent studies argue against classical systems consolidation by showing persistent hippocampal dependence of spatial memories, other work has suggested that training structure, spaced vs. massed trials, can influence this dependence. To investigate this possibility, we used DREADD-based, reversible, inhibition of MS GABAergic neurons, some of which are known to project to hippocampus. DREADD activation reduced hippocampal theta power and spatial information encoded by hippocampal neurons while largely preserving overall neuronal firing. We then examined the effect of inhibition of medial septal GABAergic neurons on learning the correct goal arm in an 8-arm maze when the correct arm was randomly changed each day. On each day, the mice were given two forced-choice trials indicating the correct arm and then 5 free-choice trials (without correction) and were always started from an opaque cylinder in the maze center, in a random orientation, to eliminate possible use of a simple response strategy. When the correct goal arm varied randomly daily, MS cell inhibition severely and repeatedly impaired acquisition. In contrast, when the correct goal arm was subsequently fixed across days, performance was initially impaired but became resistant to DREADD activation over time. Once performance reached asymptote, the goal arm was switched to a new (random) position. In this case, learning was no longer impaired by DREADD activation. This generalization suggests that repeated fixed-goal training in the same environment induces a broader reorganization of the neural systems supporting spatial behaviour. One possibility is that mice develop a septal-independent task-solving strategy that supports both retrieval of established goal locations and acquisition of new ones within a stable environment. This transition could reflect the gradual adoption of a non-spatial strategy such as visual pattern recognition, or the use of a directional cue. Moving the most salient distal cue in the environment (a single room light) produced a substantial change in the visual configurations seen from the arm entry points, and disrupted performance; however, it did not produce a consistent directional shift relative to the cue, suggesting that the light contributed to an integrated visuo-spatial representation rather than serving as the reference frame origin. We conclude that the mice switched from a hippocampus/MS-dependent spatial strategy to a non-hippocampus-dependent visual pattern matching solution.

Flexible decision making depends on internal representations that capture the latent structure of a task, allowing prior knowledge to be applied in novel circumstances. Spatial navigation provides a useful model for studying flexible choice behavior, because spatial location is itself a latent variable that must be inferred rather than directly perceived. Here, we trained rats on a navigation task that required them to reach the same goal via two distinct paths from different starting locations, and then return to one of the two starting locations before beginning the next trial. Some rats were trained to rely on distal visual landmarks, allowing task states to be identified from current sensory information, whereas others were trained to rely on path integration, requiring task states to be inferred from self-motion information accumulated over the preceding trajectory. Rats trained to rely on path integration acquired the task similarly to rats trained to rely on distal visual landmarks. However, reliance on path integration enhanced rats' ability to generalize their learning to novel situations, including finding the goal from an untrained starting location and adapting to a relocated goal that reversed learned choice sequences. These findings suggest that reliance on path integration promotes the acquisition and use of mental representations that capture the latent spatial structure of navigational tasks, thereby favoring flexible navigational decisions over rigid retrieval of reinforced responses. More broadly, our findings demonstrate how information available during training can shape representations learned from experience and thereby constrain the flexibility of decision making during inference.

Motivational incentives are known to improve working memory (WM) when items differ in value, but whether they enhance performance when all items are equally valued, and if so, by what mechanism, remains unclear. Improvements could reflect enhanced memory-based representations or speed-accuracy trade-offs, whereby incentives promote slower, more cautious responding without improving memory itself. Here, we tested these alternatives across two experiments using an auditory WM task in which incentives varied across trials, but all items on a trial were equally incentivised. In Experiment 1,we allowed participants to resubmit their responses if desired. Reward-related improvements in WM performance were selectively observed when memory load was high, and only at serial positions associated with greater interference. These improvements were also dissociated from systematic response slowing and resubmission behaviour. This indicated that the benefits of incentives were unlikely to be attributable to response caution. Critically, in Experiment 2, motivational benefits persisted under strict response deadlines, where speed cannot be traded for accuracy. Computational modelling showed that reward selectively improved the precision of memory-based responses without reducing guessing. Together, these findings indicate that motivational incentives improve WM by enhancing the quality of memory-based representations, rather than by strategic slowing or altering response strategies.

Older adults typically exhibit reduced episodic memory precision, while maintaining relatively preserved retrieval success. However, little is known about whether these age-related differences are influenced by internal biological factors (e.g., chronotype) or external testing conditions (e.g., experiment format, time of day). To address this question, younger and older adults completed an object-location memory task online, either in the morning or evening, and either with or without video-based supervision. Memory performance was assessed using mean absolute error and Bayesian hierarchical mixture modelling, which dissociated memory precision ({kappa}) from the probability of memory-based responding ({theta}). Immediate memory performance was high across age groups, irrespective of time of day. Greater encoding error predicted greater retrieval error, and participants tested in the video condition exhibited lower recall error and higher recognition performance than those tested without supervision. Consistent with prior studies, older adults exhibited reduced memory precision relative to younger adults, whereas retrieval success remained largely intact. However, Bayesian Hierarchical Modelling provided no evidence that time of day, experiment format, or their interactions with age influenced either memory precision or retrieval probability. Older adults reported stronger morning preferences than younger adults, and participants generally selected testing times that aligned with their chronotype. Nevertheless, alignment between chronotype and testing time did not modulate memory performance. The results indicate that age-related differences in episodic memory precision are robust across variations in testing context, including time of day, experiment format, and individual differences in chronotype. More broadly, the results support the feasibility of remote and unsupervised testing for memory precision research and suggest that chronotype and testing time are unlikely to be major sources of variability in immediate object-location memory performance.

Hippocampal sharp-wave ripple (SWR) events occur during post-experience rest and sleep and play a significant role in memory consolidation. Recent ex vivo studies have found orexin-driven neuromodulatory effects on SWR parameters and proposed that they can influence memory consolidation. Additionally, behavioral studies demonstrate contradictory results regarding orexinergic effects on memory acquisition depending on task structure and intervention time. This inconsistency, along with the diffuse spread of orexin receptors (OXR) in the CA1 and CA3 hippocampus, challenges theoretical interpretation of orexinergic effects on memory. To reconcile this problem, we propose a rate-based model linking orexinergic tone-dependent SWR statistics to memory performance. The model combines an encoding module whose gain scales with the global orexinergic tone with a consolidation module driven by OX2R-specific replay dynamics. The model is based on a plasticity rule that considers SWR events as the unit of induction. Therefore, weight change requires sufficient replay content and depolarizing drive. We observed that, depending on the task structure, encoding-dominant learning benefits discrimination as the orexin drive increases. Consolidation-dominant learning shows a non-monotonic relationship with an internal optimum level of orexinergic tone. This interaction highlights that stronger truncation at higher receptor engagement shortens memory replay and reduces the efficacy of the consolidation process. The model predicts that the optimal regime depends on task complexity reflected in sequence length. Together, these results demonstrate how task demands determine whether increased orexinergic drive enhances or impairs effective consolidation and SWR-dependent replay in the hippocampus.

The toxicity of chemical defences is well studied, but the potential contribution of compound structure to predator deterrence remains largely unexplored. Whether predation acts more strongly on toxicity or unpalatability remains largely untested, partly because few systems allow toxin structure to vary independently of quantity. Heliconius sara larvae provide such a system: those reared on Passiflora auriculata sequester cyclopentenyl cyanogenic glucosides (CGs), while those reared on P. biflora biosynthesise comparable quantities of aliphatic CGs. Using two invertebrate predators, Camponotus floridanus ants and Hierodula membranacea mantids, we tested whether this structural difference affects palatability independent of toxicity. Mantids rejected larvae with cyclopentenyl CGs more often than larvae with aliphatic CGs, despite no detectable difference in total CG content. This pattern was mirrored in extract-based assays with ants, independently of cyanide release: extracts with cyclopentenyl CGs remained deterrent, while extracts with aliphatic CGs did not differ in deterrence from water. Live larvae, by contrast, elicited similar responses from ants regardless of CG structure. These results show that variation in toxin structure can strongly affect palatability, with some compounds conferring greater protection than others. This demonstrates the importance of chemical structural diversity in the evolution of chemical defences.

Recalling scenes and events depends on how information is relationally organised in memory, but it is unclear whether the organisation of eye movements during encoding, rather than simply how much is explored, shapes what is remembered. Using a scene-viewing paradigm and drawing-based free recall task to capture the content and structure of remembered scenes, we examined whether scene memory was better explained by 'lower-order' measures reflecting the magnitude and spatial extent of sampling, or 'higher-order' measures capturing gaze organisation and temporal dynamics. Relative to lower-order measures (number of fixations and scanpath length), memory precision was better predicted by repeated sampling of viewed regions (refixations) and gaze distributions (stationary gaze entropy) during encoding. Thus, the organisation of visual attention, rather than sampling quantity, contributed to scene representations that preserved relationships between elements. These findings highlight a role for spatial gaze dynamics in optimally encoding organised, relational scene representations for episodic memory.

Animal behaviour is both innately constrained and shaped by learning. This mosaic organization has evolved in response to species-specific ecological demands and may differ between sensory modalities. Flower-visiting animals are a particularly useful system for investigating the relationship between sensory ecology and learning because they rely on multiple floral cues, particularly odour and colour, to locate food sources. However, it remains largely unexplored whether specialization on floral resources entails divergence in learning abilities across sensory modalities. Drosophila elegans is a flower-feeding species that depends heavily on floral resources throughout its life; adults spend much of their time on flowers and larvae develop on fallen flower leaves. Here, we compared odour-reward and colour-reward associative learning between the flower-feeding D. elegans and the fruit-feeding D. melanogaster. We found that, under conditions of equilibrated motivation, odour- and colour-preference, and using the same sugar reward, D. elegans exhibited poorer odour-reward learning performance but better colour-reward learning performance than D. melanogaster. These results suggest that the modality-specific eligibility of sensory information to enter into associations, known as the 'Garcia-effect' in experimental psychology, can evolve oppositely between species. This highlights the relationship between ecological specialization and mnemonic processing, and shows that biological 'intelligence' is not general.

Although dementias primarily affect memory, they also disrupt our closest social relationships, resulting in elevated caregiver burden and worse patient outcomes. However, the mechanistic study of how pathology affects social attachments is limited by the use of laboratory rodents that do not form selective, long-term bonds. Here, in monogamous prairie voles, we expressed dementia-causing tauP301L in the paraventricular hypothalamus of 12- and 18-month-old animals, and separately, from birth through 18-months, across hippocampocortical regions. Hippocampocortical expression of tauP301L did not yield deficits in social or non-social dementia-related phenotypes. In contrast, tauP301L expressed in the hypothalamus yielded sex- and age-dependent social bonding deficits. 18-month males with hypothalamic tau pathology failed to form bonds and displayed blunted sociability, effects that converged across bonding assays. In addition, healthy 18-month males paired with a hypothalamic tau-expressing female also showed reduced partner preference, suggesting that pathology exerts vicarious effects on partners. Social behavior of both healthy females and those expressing tauP301L were unaffected. 18-month tauP301L males also showed elevated oxytocin fluorescence. These findings establish direct and vicarious disruptions to pair bonding induced by hypothalamic tau pathology in male prairie voles, potentially via altered oxytocin signaling.

It is estimated that approximately fifty percent of the population will encounter at least one traumatic event during their lifetime; however, only six percent develop Posttraumatic Stress Disorder (PTSD), a trauma-related disorder characterized by persistent alterations in affect and cognition, including an exaggerated fear response. It is well established that females (9.7%) are more than twice as likely as males (3.6%) to be diagnosed with PTSD. Nevertheless, a significant challenge remains in understanding how the severity of traumas experienced in childhood versus adulthood influences PTSD development across sexes. To address this challenge effectively, the adoption of preclinical animal models that accurately reflect these key characteristics is crucial. The Stress Enhanced Fear Learning (SEFL) paradigm in rodents encapsulates some of these complexities associated with PTSD, such as persistent fear sensitization following exposure to acute trauma. This study investigates how stress severity and developmental timing affect the long-term maintenance of SEFL in male and female rats. Juvenile and adult rats were initially subjected to no stress (control, context only), low stress (1 footshock), moderate stress (3 footshocks), or high stress (15 footshocks), followed by an extinction session either one day (recent) or sixty days (remote) later. Subsequently, to evaluate SEFL in a new context, all subjects received a single footshock and were tested the following day. Shortly after stress induction, all groups displayed SEFL. Although the effects persisted for sixty days in adult males and juvenile females, even at the lowest stress level, they were significantly reduced in juvenile males and adult females. These findings offer novel insights into sex-related differences in the persistence of SEFL and introduce new considerations regarding how the timing of developmental stressors influences future threat encoding and fear responses.

Infantile amnesia refers to the loss of event-based memories acquired early in life. In mice, however, these memories are not erased; selective optogenetic stimulation of engrams formed in infancy leads to memory recovery in adulthood, indicating that infant-formed engrams can persist in a latent form. We therefore asked whether these latent engrams, although not accessible through natural retrieval, nonetheless influence related adult learning. Using a contextual fear conditioning paradigm, we find that adult learning is facilitated by prior experience in infancy, both for the same and related contexts. Activity-dependent engram tagging revealed that adult learning reactivates infant-acquired dentate gyrus ensembles, and selective inactivation of these ensembles during adulthood abolished this facilitation. These findings indicate that memories formed in infancy persist as latent engrams that scaffold subsequent learning, consistent with a role in establishing schema-like representations.

Pattern separation and pattern completion are core hippocampal computations linked to memory interference and overgeneralization in many neuropsychiatric disorders and to mnemonic discrimination deficits in neurodegenerative conditions. Astrocytes are increasingly recognized as important integrators and modulators of neuronal activity as many studies have shown changes in animal behavior and neural circuits induced by manipulation of astrocytic activity. The role of astrocytes in the dentate gyrus for learning and memory is, however, largely unknown. To investigate the functional significance of astrocytic activity in the dentate gyrus, we expressed the calcium extruding pump hPMCA2w/b (CalEx), resulting in inhibition of astrocytic calcium activity, the Gq-coupled receptor hM3Dq, or the Gi-coupled receptor hM4Di, allowing chronic activation of Gq- and Gi-dependent pathways by a designer drug, in dentate gyrus astrocytes. Our main finding is that inhibition of astrocytic calcium activity by CalEx resulted in improved pattern separation and impaired pattern completion. In -vivo calcium imaging revealed that CalEx expression in astrocytes altered the neuronal activity pattern in dentate gyrus neurons with an overall inhibitory effect. This suggests that in the dentate gyrus astrocytes promote the activity of these neurons. Furthermore, chronic activation of hM4Di resulted in impaired between-session fear extinction while chronic activation of hM3Dq resulted in impaired within-session fear extinction and improved pattern separation learning over multiple days, suggesting that activation of astrocytic activity enhances mechanistically separable forms of fear extinction in a Gq- or Gi-pathway-specific manner. Our findings reveal that dentate gyrus astrocytic calcium shifts the balance between pattern separation and pattern completion towards pattern completion and thus modulates an essential neuronal functional output of the dentate gyrus. Chronic activation of astrocytes inhibits fear extinction, and thus also affects management of memory interference. Our findings imply that astrocytic modulation may be beneficial to treat cognitive deficits in disorders in which overgeneralization is a problem.

Hypothalamic supramammillary nucleus (SuM) neurons project to the dentate gyrus and co-release glutamate and GABA, thereby regulating hippocampal information processing. However, how synapses mediating glutamate/GABA co-transmission are established during development remains unclear. Here, we investigated the functional and structural maturation of SuM inputs onto adult-born granule cells (GCs). We found that most newborn GCs received GABAergic responses without detectable glutamatergic responses, whereas a smaller population exhibited glutamate/GABA co-transmission. Newborn GCs with glutamate/GABA co-transmission showed more mature anatomical and physiological properties than GABA-only neurons, with greater dendritic complexity, longer dendritic length, lower input resistance, and stronger medial perforant path inputs. Postsynaptic depolarization failed to induce synapse unsilencing in GABA-only neurons but induced robust long-term potentiation in newborn GCs with glutamatergic transmission, indicating that plasticity at SuM inputs emerges after functional glutamatergic transmission is established. Morphological analysis showed that SuM terminals apposed to newborn GCs contained both VGluT2 and VIAAT, whereas postsynaptic receptor organization remained immature. Moreover, environmental enrichment and chemogenetic activation of SuM neurons increased the proportion of newborn GCs receiving glutamate/GABA co-transmission, suggesting that SuM activity promotes the emergence of glutamatergic transmission. Together, these results suggest that SuM inputs onto newborn GCs undergo sequential maturation from initial GABAergic transmission to glutamate/GABA co-transmission, a process likely supported by SuM activity-dependent postsynaptic maturation.

Early-life adversity is associated with highly variable developmental outcomes, but identifying sources of this heterogeneity is difficult because variation in outcome is typically accompanied by variation in exposure. Animal models provide experimental leverage by standardizing features of the early environment while allowing variation in developmental experience and outcome to remain observable. Using a graded limited bedding and nesting model spanning normative rearing, moderate restriction, and severe scarcity, we asked what distinguishes social outcomes among animals exposed to the same resource restriction. Severe scarcity increased adverse maternal handling while leaving organized nurturing behaviors intact. Following the P8-P12 rearing manipulation, pups were tested outside the home cage in a P13 social approach assay. Severe scarcity reduced the proportion of pups that approached the dam, but outcomes varied substantially among scarcity litters. Greater typical maternal pup transport predicted greater approach, whereas a greater proportion of rough transport predicted poorer approach. Transport composition did not differ across rearing conditions, but its relationship with social behavior did. Amygdala intercalated-cell recruitment also covaried with social approach under severe scarcity despite limited condition-level differences in regional c-Fos. Plasma corticosterone differed across rearing conditions but did not covary detectably with the principal caregiving, behavioral, or neural measures. Maternal transport and intercalated-cell recruitment were not robustly associated, identifying separable experiential and neural correlates of behavioral variation. These findings show that standardizing an environmental constraint does not produce uniform developmental experience or outcome, and that caregiving experiences preserved across rearing conditions can distinguish social outcomes under severe scarcity.

The small GTPase Rem2 is a key signaling molecule involved in synaptic formation, dendritic complexity, spine formation, and regulation of CaMKII-dependent long-term potentiation (LTP). However, it remains unclear how Rem2 explicitly impacts learning and memory. To address this issue, we deleted Rem2 specifically in dorsal CA1 neurons of male and female mice and assessed spatial learning using a spatial object recognition (SOR) task. We found that males outperform females in this behavioral assay and that deleting Rem2 did not impact spatial learning in males. In contrast, Rem2 deletion significantly improved spatial learning in females enabling them to perform as well as males in the SOR task. Using an automated Western blot system to assess all known AMPA- and NMDA-mediated glutamate receptor (AMPAR and NMDAR) subunits in each mouse, we found that the sex-dependent change in SOR we observed was likely due to Rem2 increasing GluN2D expression in the interneurons of female mice only. Furthermore, using S-statistics to compare the overall AMPAR and NMDAR composition among groups, we found that males and females normally have divergent covariance structures but this divergence is eliminated when Rem2 is deleted from CA1 neurons. These results reveal an unexpected role of Rem2 in maintaining sex differences in glutamate receptor composition and spatial learning abilities. To our knowledge, this is the first demonstration of a signaling molecule that confers sexual dimorphism to excitatory synapses. As such, Rem2 may play a critical role in understanding how sex-dependent symptoms of neurodevelopmental and neurodegenerative disorders arise.

Exploration is fundamental to how children learn about the world. To explore a new environment comprehensively, a child must navigate without getting lost while simultaneously attending to salient information along the way. Both abilities improve across childhood, yet most studies examine them in isolation, often in constrained spaces with limited sensory complexity. Here, we asked 7- to 14-year-old children (N=42) and young adults (18-22; N=42) to freely explore a large furniture store in immersive virtual reality, which contained many objects and attention-capturing multisensory events. Surprisingly, despite traveling comparable distances, children explored less - they covered less spatial area and examined fewer unique objects than adults. Fine-grained analyses of their behaviors showed that the reduction in exploration was due to children spending more time backtracking and children taking longer to adapt to salient multisensory objects, which were uncorrelated across individuals after controlling for age and independently predicted exploration. However, only backtracking duration predicted success in a subsequent search task, demonstrating a link between navigational success during exploration and the quality of learned spatial representations for later use. Together, the results demonstrate that children explore less comprehensively than adults in large-scale spaces because they are susceptible to getting lost and perseverating on salient events nested within a large environment, but that these behaviors change with age. This suggests that while children are widely considered to be curious explorers within local environments, their ability to do so within larger environments is shaped by the maturation of cognitive systems that integrate experiences over complex contexts.

Making choices about whether and when to engage cognitive effort is a common feature of human everyday experience with important consequences for academic, career, and health outcomes. Yet, despite its importance, little is understood about the neurochemical mechanisms that underlie individual differences in the willingness to engage in cognitively effortful activities. To examine this question, we employed a multi-modal neuroimaging approach in which participants performed the Cognitive Effort Discounting paradigm (Cog-ED) while simultaneous PET-fMRI was acquired. We assessed both individual differences in dopamine-D2 receptor availability and brain activity during decision-making. In addition, the same participants performed a parametric working memory task (N-Back) and reported the cognitive effort associated with their daily life activities through a seven-day Ecological Momentary Assessment (EMA) protocol. The findings suggest a central role for caudate dopamine-D2 receptors in modulating cognitive effort-related motivation. People with higher caudate dopamine-D2 receptor availability had better working memory function, heightened sensitivity to effort costs, and greater modulation of brain activity during effort valuation. These laboratory findings also translated directly to daily life: higher levels of caudate dopamine-D2 receptors were associated with greater engagement in cognitively effortful activities. Together, the results suggest that how individuals determine the motivational value of cognitively effortful activities strongly depends on the dopamine system.

Attentional selection not only increases behavioural performance and neural information for attended stimuli but, in some instances, induces changes in stimulus appearance. While reported appearance changes have mostly concerned the effects of attending to a particular spatial location, here we report a shift in appearance that occurs when attention is directed to one component of a stimulus rapidly alternating at a single spatial location. Our stimuli included two frames of different colors, which alternated at 3.75Hz or 7.5Hz. Participants reported the perceived dominance of one frame's color in the reference stimulus, by comparison with a target stimulus. We found that when one stimulus frame was more salient than the other, with a greater likelihood of capturing exogenous attention, there was an illusory perception that the frame was physically present for a greater proportion of time. When the frames were matched in salience, a task encouraging participants to endogenously direct their attention to one frame produced a smaller shift in appearance. Our results add to the body of literature demonstrating that attention can change appearance, in this case altering the appearance of attended versus unattended stimuli that are presented at the same spatial location. Furthermore, our results demonstrate that at the 'temporal transparent' alternation rate of 7.5Hz, where rapidly alternating stimuli are perceived as two translucent surfaces, attentional selection of one surface can account for the apparent paradox that feature conjunctions are perceived at stimulus alternation rates higher than predicted by the temporal limits of feature binding for other stimuli.