Time Of Day Effects Research Articles

Community modeling reveals the importance of elevation and land cover in shaping migratory bird abundance in the Andes.

The tropical Andes are characterized by extreme topographic and climatic complexity, which has likely contributed to their outstanding current species diversity, composed of many range‐restricted species. However, little is known about how the distribution and abundance of highly mobile organisms, like long‐distance migratory birds, varies across different land covers, elevations, and climatic conditions within the Andes. We conducted 1,606 distance‐sampling point counts across the Colombian Andes, spanning elevations from 253 to 3,708 m, a range of precipitation regimes and representative land covers. We then employed a novel application of a multispecies hierarchical modeling approach to evaluate how elevation, local land cover, aboveground woody biomass, cloud cover, precipitation, and seasonality in precipitation shape the abundance of the migratory land bird community in the Andes. We detected 1,824 individuals of 29 species of migratory land birds, six of which were considered incidental in our study region. We modeled the abundance of the remaining 23 species, while considering observer and time of day effects on detectability. We found that both elevation and land cover had an overriding influence on the abundance of migratory species across the Andes, with strong evidence for a mid‐elevation peak in abundance, and species‐specific responses to both variables. As a community, migratory birds had the highest mean abundance in shade coffee plantations, secondary forest, and mature forest. Aboveground woody biomass did not affect the abundance of all species as a group, but a few showed strong responses to this variable. Contrary to predictions of a positive correlation between abundance and precipitation, we found no evidence for community‐level responses to precipitation, aside for a weak tendency for birds to select areas with intermediate levels of precipitation. This novel use of a multispecies model sheds new light on the mechanisms shaping the winter distribution of migratory birds and highlights the importance of elevation and land cover types over climatic variables in the context of the Colombian Andes.

Sharper in the morning: Cognitive time of day effects revealed with high-frequency smartphone testing

ABSTRACT Decades of research has established a shift from an “eveningness” preference to a “morningness” preference with increasing age. Accordingly, older adults typically have better cognition in morning hours compared to evening hours. We present the first known attempt to capture circadian fluctuations in cognition in individuals at risk for Alzheimer disease (AD) using a remotely administered smartphone assessment that samples cognition rapidly and repeatedly over several days. Older adults (N = 169, aged 61–94 years; 93% cognitively normal) completed four brief smartphone-based testing sessions per day for 7 consecutive days at quasi-random time intervals, assessing associate memory, processing speed, and visual working memory. Scores completed during early hours were averaged for comparison with averaged scores completed during later hours. Mixed effects models evaluated time of day effects on cognition. Additional models included clinical status and cerebrospinal fluid (CSF) biomarkers for beta amyloid (Aβ42) and phosphorylated tau181 (pTau). Models with terms for age, gender, education, APOE ε4 status, and clinical status revealed significantly worse performance on associate memory in evening hours compared to morning hours. Contemporaneously reported mood and fatigue levels did not moderate relationships. Using CSF data to classify individuals with and without significant AD pathology, there were no group differences in performance in morning hours, but subtle impairment emerged in associate memory in evening hours in those with CSF-confirmed AD pathology. These findings indicate that memory is worse in evening hours in older adults, that this pattern is consistent across several days, and is independent of measures of mood and fatigue. Further, they provide preliminary evidence of a “cognitive sundowning” in the very earliest stages of AD. Time of day may be an important consideration for assessments in observational studies and clinical trials in AD populations.

Time of day effect on biomarkers of exposure to pesticides during an isopesticide time-restricted diet: a pilot randomized trial

BACKGROUND AND AIM: The role of the circadian liver clock in shaping the metabolism of dietary pesticides and their downstream biological effects remains poorly understood in real-life human settings. This trial aimed to investigate whether the consumption of fruits and vegetables within a specific time-restricted window of the day would affect the magnitude and variance of biomarkers of exposure to pesticides. METHODS: CIRCA CHEM is a randomized 2x2 cross-over chronotoxicity pilot trial. All participants (n=45) were randomly allocated to two groups and asked to daily adhere to an isopesticide dietary pattern consuming four fruits portions and two vegetable portions at specific time-restricted windows. The first group was asked to adhere to a week-long morning time-restricted window (9am-12pm) and after a week’s washout to cross over to the evening time-restricted period for another week (7pm-10pm) and vice-versa for the other group. Anthropometrics measurements were obtained and urinary biomarkers of exposure to neonicotinoids (6-chloronicotinic acid, 6-CN) and pyrethroids (3-phenoxybenzoic acid, 3-PBA) pesticides were measured using mass spectrometry. Linear mixed effect models will be used to model the time of day effects on the biomarkers of exposure to pesticides. RESULTS:A total of 41 healthy adults with mean age of 36 years old were included in the analysis. Overall fruit and vegetable daily intake adherence to the pre-specified time-restricted periods by the participants was high (80%) in both groups. No difference in anthropometric measurements (weight, BMI, waist circumference) was observed for both groups by the end of the study. The diurnal variation in the 3-PBA and 6-CN biomarkers will be presented, including the effect of time of the day of fruits/vegetables consumption on the magnitude of these biomarkers CONCLUSIONS:This pilot trial will shed light on possible chronotoxicity trends associated with fruits/vegetables-based exposures to pesticides. KEYWORDS: biomarkers of exposure, pesticides, food/nutrition, chemical exposures, exposure assessment, exposome

Circadian asthma airway responses are gated by REV-ERBα.

The circadian clock powerfully regulates inflammation and the clock protein REV-ERBα is known to play a key role as a repressor of the inflammatory response. Asthma is an inflammatory disease of the airways with a strong time of day rhythm. Airway hyper-responsiveness (AHR) is a dominant feature of asthma; however, it is not known if this is under clock control. To determine if allergy-mediated AHR is gated by the clock protein REV-ERBα. After exposure to the intra-nasal house dust mite (HDM) allergen challenge model at either dawn or dusk, AHR to methacholine was measured invasively in mice. Wild-type (WT) mice show markedly different time of day AHR responses (maximal at dusk/start of the active phase), both in vivo and ex vivo, in precision cut lung slices. Time of day effects on AHR were abolished in mice lacking the clock gene Rev-erbα, indicating that such effects on asthma response are likely to be mediated via the circadian clock. We suggest that muscarinic receptors one (Chrm 1) and three (Chrm 3) may play a role in this pathway. We identify a novel circuit regulating a core process in asthma, potentially involving circadian control of muscarinic receptor expression, in a REV-ERBα dependent fashion. These insights suggest the importance of considering the timing of drug administration in clinic trials and in clinical practice (chronotherapy).

A Bayesian Markov Model with Pólya-Gamma Sampling for Estimating Individual Behavior Transition Probabilities from Accelerometer Classifications

The use of accelerometers in wildlife tracking provides a fine-scale data source for understanding animal behavior and decision-making. Current methods in movement ecology focus on behavior as a driver of movement mechanisms. Our Markov model is a flexible and efficient method for inference related to effects on behavior that considers dependence between current and past behaviors. We applied this model to behavior data from six greater white-fronted geese (Anser albifrons frontalis) during spring migration in mid-continent North America and considered likely drivers of behavior, including habitat, weather and time of day effects. We modeled the transitions between flying, feeding, stationary and walking behavior states using a first-order Bayesian Markov model. We introduced P\'olya-Gamma latent variables for automatic sampling of the covariate coefficients from the posterior distribution and we calculated the odds ratios from the posterior samples. Our model provides a unifying framework for including both acceleration and Global Positioning System data. We found significant differences in behavioral transition rates among habitat types, diurnal behavior and behavioral changes due to weather. Our model provides straightforward inference of behavioral time allocation across used habitats, which is not amenable in activity budget or resource selection frameworks.

0311 The Impairments in Emotional Perception Following Total Sleep Deprivation and the Restorative Effects of Napping and Time of Day

Abstract Introduction The ability to perceive emotions is a socially-relevant skill critical for healthy interpersonal functioning, while deficits in this ability are associated with psychopathology. Total sleep deprivation (TSD) has been shown to have deleterious effects on emotion perception, yet the extent to which these impairments persist across the day with continued wakefulness, or if brief periods of recovery sleep can restore emotion perception abilities, remains unexplored. Methods Participants viewed slideshows of faces ranging in emotional expression and were asked to categorize (Happy, Sad, Angry, Neutral) and rate the emotional intensity (1-9) of each face at baseline (2100; Session 1), at 0900 (Session 2) following a night of sleep or TSD, and at 1400 (Session 3) following either continued wakefulness (wake group) or a 90-minute nap opportunity (nap group). Results Emotion categorization ability marginally improved from Session 1 to Session 2 following overnight sleep, however, no changes in emotion intensity ratings or vigilance were observed. TSD led to an increase in error rates during vigilance testing [t(46)=2.9, p=0.005] and impairment in emotion categorization ability [t(46)=5.5, p<0.001] from Session 1 to Session 2, although by Session 3 performance levels on both measures returned to baseline for all TSD participants. TSD also led to a decrease in emotional intensity ratings from Session 1 to Session 2, particularly for the highest tertile of emotional faces [6-9; t(46)=6.1, p<0.001]. These ratings remained suppressed at Session 3 in both the wake [t(25)=7.8, p<0.001] and nap [t(18)=3.1, p=0.006] groups. Conclusion These results indicate that time of day effects, with or without any additional benefit of a nap, can restore the impairments in vigilance and emotional categorization caused by TSD. The ability to discriminate levels of emotional intensity, however, is not restored by time of day or napping, suggesting that this ability is more sensitive to the impact of TSD. Support

Diurnal Timing Dependent Alterations in Gut Microbial Composition Are Synchronously Linked to Salt-Sensitive Hypertension and Renal Damage.

Alterations of diurnal rhythms of blood pressure (BP) and reshaping of gut microbiota are both independently associated with hypertension. However, the relationships between biorhythms of BP and gut microbial composition are unknown. We hypothesized that diurnal timing-associated alterations of microbial compositions are synchronous with diurnal rhythmicity, dip in BP, and renal function. To test this hypothesis, Dahl salt-sensitive (S) rats on low- and high-salt diets were examined for time of day effects on gut microbiota, BP, and indicators of renal damage. Major shifts in night and day patterns of specific groups of microbiota were observed between the dark (active) and light (rest) phases, which correlated with diurnal rhythmicity of BP. The diurnal abundance of Firmicutes, Bacteroidetes, and Actinobacteria were independently associated with BP. Discrete bacterial taxa were observed to correlate independently or interactively with one or more of the following 3 factors: (1) BP rhythm, (2) dietary salt, and (3) dip in BP. Phylogenetic Investigation of Communities revealed diurnal timing effects on microbial pathways, characterized by upregulated biosynthetic processes during the active phase of host, and upregulated degradation pathways of metabolites in the resting phase. Additional metagenomics functional pathways with rhythm variations were noted for aromatic amino acid metabolism and taurine metabolism. These diurnal timing dependent changes in microbiota, their functional pathways, and BP dip were associated with concerted effects of the levels of renal lipocalin 2 and kidney injury molecule-1 expression. These data provide evidence for a firm and concerted diurnal timing effects of BP, renal damage, and select microbial communities.

Time of day is associated with paradoxical reductions in global signal fluctuation and functional connectivity.

The brain exhibits substantial diurnal variation in physiology and function, but neuroscience studies rarely report or consider the effects of time of day. Here, we examined variation in resting-state functional MRI (fMRI) in around 900 individuals scanned between 8 AM and 10 PM on two different days. Multiple studies across animals and humans have demonstrated that the brain's global signal (GS) amplitude (henceforth referred to as "fluctuation") increases with decreased arousal. Thus, in accord with known circadian variation in arousal, we hypothesised that GS fluctuation would be lowest in the morning, increase in the midafternoon, and dip in the early evening. Instead, we observed a cumulative decrease in GS fluctuation as the day progressed. Although respiratory variation also decreased with time of day, control analyses suggested that this did not account for the reduction in GS fluctuation. Finally, time of day was associated with marked decreases in resting-state functional connectivity across the whole brain. The magnitude of decrease was significantly stronger than associations between functional connectivity and behaviour (e.g., fluid intelligence). These findings reveal time of day effects on global brain activity that are not easily explained by expected arousal state or physiological artefacts. We conclude by discussing potential mechanisms for the observed diurnal variation in resting brain activity and the importance of accounting for time of day in future studies.

Habitual Sleep, Social Jetlag, and Reaction Time in Youths With Delayed Sleep–Wake Phase Disorder. A Case–Control Study

The aim of this study was to explore habitual sleep, social jetlag, and day-to-day variations in sleep (measured as intra-individual standard deviation, ISD) in youths with delayed sleep–wake phase disorder (DSWPD), compared to healthy controls. We also aimed to investigate time of day effects in performance. The sample comprised 40 youths with DSWPD (70.0% female, mean age 20.7 ± 3.1 years) and 21 healthy controls (71.4% female, mean age 21.2 ± 2.2 years). Subjective and objective sleep were measured over 7 days on a habitual sleep schedule by sleep diary and actigraphy recordings. Performance was tested twice with a 12-h interval (22:00 in the evening and 10:00 the following morning) using a simple, 10-min sustained reaction time test (RTT). The results showed later sleep timing in the DSWPD group compared to the controls, but sleep duration, social jetlag, and ISD in sleep timing did not differ between the groups. Still, participants with DSWPD reported longer sleep onset latency (SOL) and poorer sleep efficiency (SE), sleep quality, and daytime functioning, as well as larger ISD in SOL, sleep duration, and SE. The groups had similar evening performances on the RTT, but the DSWPD group performed poorer (slower with more lapses) than the controls in the morning. The poor morning performance in the DSWPD group likely reflects the combined impact of sleep curtailment and circadian variations in performance (synchrony effect), and importantly illustrates the challenges individuals with DSWPD face when trying to adhere to early morning obligations.

The 3-minute Psychomotor Vigilance Task (PVT) Embedded in a Wrist-worn Device: Time of Day Effects

The study assesses the utility of the 3-minute version of the Psychomotor Vigilance Task (PVT) embedded in a wrist-worn device (interstimulus interval – ISI =1 - 4 seconds) to detect changes in performance between a morning and an afternoon data collection session. The experiment utilized a randomized, within-subject, repeated-measures design with two factors, device type (wrist-worn PVT, laptop PVT, Go/No-Go task) and time of day (morning, afternoon). Results showed that performance in both the wrist-worn 3-minute PVT (ISI = 1 – 4 seconds) and the 5-minute Go/No-Go task (180 trials, 80% Go/20% No Go; ISI = 0.5 – 1.0 seconds) differed between the morning and the afternoon sessions but not the laptop-based PVT. We discuss these findings under the light of the differences in task characteristics between the wrist-worn and the laptop PVT

The correlation between education, engineering, enforcement, and self-reported seat belt use in Tennessee: Incorporating heterogeneity and time of day effects

Time of day and heterogeneity are two common factors that received less attention in self-reported studies concerning seat belt use. Although nighttime seat belt use rate is relatively lower than daytime, previous studies have often not separated the analysis of seat belt use between daytime and nighttime. To incorporate heterogeneity in our analysis, we used random parameters and geographically weighted regression models to explore the factors influencing seat belt use. This study consists of a self-reported seat belt use survey conducted in a sample of 814 respondents aged 18–50 years in six counties (50 zip codes area) in East Tennessee. Comparison of the models indicated that the geographically weighted regression models outperformed other models. Considering the non-stationary test, we learned that the local coefficients displayed relatively constant variation across space in the study area, which indicates behaviors, at least across a large metropolitan area, does not vary spatially. For the random parameter models, age and income had random parameter effects. Perception of receiving a ticket for not wearing a seat belt, uncomfortable seat belt design, driving for a short distance, and driving exposure also had significant negative associations with self-reported seat belt use in both models. Moreover, exposure to educational programs had a significant correlation with seat belt use only in nighttime, whereas this correlation was insignificant for daytime. Findings provide new insight for design and convoy new messages to promote seat belt use by targeting factors predicting seat belt use. Results are discussed in line with road safety analysis.

Evaluation of the time-of-day effect of herbicides applied POST on protoporphyrinogen IX oxidase–resistant and –susceptible Palmer amaranth (Amaranthus palmeri)

AbstractStudies to evaluate the effect of application time of day (TOD) and protoporphyrinogen IX oxidase (PPO)-inhibiting herbicide–resistant Palmer amaranth on the efficacy of commonly used herbicides was conducted in Tennessee in 2017 and 2018. Treatments of fomesafen, lactofen, acifluorfen, paraquat, glufosinate, glufosinate plus fomesafen, paraquat plus fomesafen, and paraquat plus metribuzin were applied to PPO-resistant (PPO-R) and PPO-susceptible (PPO-S) Palmer amaranth at sunrise and midday. Control of Palmer amaranth with acifluorfen, glufosinate, and glufosinate plus fomesafen was greater with the midday application. However, control of Palmer amaranth with paraquat-based treatments was greater with the sunrise application. TOD effects on PPO-inhibiting herbicides and paraquat-based treatments were more prominent for the PPO-R Palmer amaranth biotype. The TOD effect observed when applying glufosinate in early morning hours on PPO-S Palmer amaranth can be minimized by adding fomesafen to the tank mix. However, this strategy did not provide consistent performance on PPO-R Palmer amaranth. The percentages of living Palmer amaranth plants and control were greater when paraquat plus metribuzin was applied to both biotypes. These results highlight the necessity of at least two effective herbicide sites of action for POST applications intended for controlling PPO-R Palmer amaranth. In addition, the timing of herbicide applications can affect their activity in both PPO-R and PPO-S Palmer amaranth populations.

Time of Day Effects on Peanut Herbicide Efficacy

ABSTRACT Recent research on the effects of time of d (TOD) when glufosinate is applied to cotton (Gossypium hirsutum L.) and several protoporphyrinogen-inhibiting herbicides in soybean (Glycine max L.) has growers concerned about potential TOD effects on peanut weed control. Consequently, research was conducted in 2015, 2016, and 2017 to determine if TOD influences the performance of peanut herbicides acifluorfen, bentazon, imazapic, lactofen, paraquat, and 2,4-DB. Both non- (bare-ground) and in-crop (peanut) studies were conducted. For non-crop, paraquat plus bentazon plus acifluorfen plus S-metolachlor, imazapic plus S-metolachlor plus 2,4-DB, and lactofen plus S-metolachlor plus 2,4-DB were applied to Palmer amaranth and a non-uniform mixture of annual grasses including Urochloa texana (Buckley), Dactyloctenium aegyptium (L.), Eleusine indica (L.), Digitaria spp. at 7:00, 12:00, 17:00, and 22:00 hr. For in-crop studies, two peanut weed control programs were used and herbicide programs were applied at the same TOD. Herbicides were paraquat plus acifluorfen plus bentazon plus S-metolachlor (EPOST) followed by imazapic plus S-metolachlor plus 2,4-DB, or lactofen plus S-metolachlor plus 2,4-DB (POST). For the non-crop studies, a significant interaction between TOD and herbicide program was observed for the 7 d after treatment (DAT) rating of Palmer amaranth control. Control was reduced with imazapic applied at 22:00 hr. At 14 DAT, there was no TOD effect and control was reduced with all imazapic treatments due to ALS resistance. There was no interaction between TOD and herbicide program for annual grass control. Annual grass control was unacceptable (<50%) with lactofen. For in-crop studies, there was no interaction between TOD or herbicide program. Peanut injury was lower at 7:00 hr and 22:00 hr when compared to other timings. Lactofen was more injurious to peanut than imazapic. Palmer amaranth control was not influenced by timing or herbicide program. A reduction in sicklepod control was observed at the 22:00 hr timing and with lactofen. While TOD influenced peanut injury and weed control, peanut yield was not affected.

Time of day effects of temperature and daylight on short term electricity load

Abstract This paper proposes a model for short-term electricity load with differentiated temperature and daylight effects by time of day, which are determined by variations in intraday economic activity. The relationship between electricity load and economic activity implies that the electricity demand response to changes in exogenous variables like temperature is non-linear as well as non-homogeneous along the day. The proposed framework, a smooth transition regression model with double threshold (LSTR2), models the observed intraday patterns in load curves to explicitly capture the effect of the circadian rest-activity cycle on the distinct responses of electricity demand to temperature and daylight variations throughout the day. The model shows that the sensitivity of demand to low temperatures is significantly larger in the “active” compared to the “rest” state. If temperatures decrease from 10 °C to 0 °C, electricity demand in the “active” state increases by 960.5 MW h per 1 °C decrease, but by only 26.6 MW h per 1 °C decrease in the “rest” state. When temperatures are higher, in the “rest state” demand decreases by 602.9 MW h per 1 °C if temperature falls from 26 °C to 21 °C, while in the “active” state demand only decreases by 323.6 MW h per 1 °C variation.

Does exercising at a certain time-of-day affect athletes skeletal muscle damage markers? A systematic review and meta-analysis

The objective of the study was to examine time of day effects of exercise on athletes’ skeletal muscle damage markers. The skeletal muscle damage marker enzymes like creatine kinase, lactate dehydr...

Hypothalamic-pituitary-adrenal axis differentially responses to morning and evening psychological stress in healthy subjects.

AimThe hypothalamic‐pituitary‐adrenal (HPA) axis responds to changing environmental demands including psychological stressors. The aim of the present study was to assess whether the time of day effects on the acute response of HPA axis activity to acute psychological stress.MethodWe studied 27 healthy young subjects. The subjects were participated two experiments as follows. In the first experiment, subjects were instructed to keep their regular sleep schedule for 2 weeks which were measured by using a wrist‐worn activity monitor. Afterward, to evaluate a diurnal rhythm of salivary cortisol, eight saliva samples were collected during waking period every 2 hours from when the subjects woke up. In the second experiment, the subjects were randomly assigned to two groups. The Trier Social Stress Test (TSST) was performed either in the morning (n = 14) or in the evening (n = 13). We measured diurnal rhythm of salivary cortisol and stress response of salivary cortisol and heart rate by the TSST. Morning and evening tests were started at 2 hours and 10 hours after woke up, respectively.ResultsAll subjects showed a normal diurnal rhythm of salivary cortisol concentration, with a peak in the morning immediately after awaking and a minimum in the evening. The salivary cortisol response after the TSST was significantly increased from the prestress level in the morning but not in the evening.ConclusionThe HPA response to acute psychological stress was more pronounced in the morning than in the evening, correlating with the circadian regulation of cortisol synthesis.

Time of day effects on the relationship between daily sleep and anxiety: An ecological momentary assessment approach

Previous research has linked sleep disturbance to anxiety. However, evidence for this relation has been inconsistent, largely limited to retrospective reports that do not account for daily variability, and silent on when the association is most pronounced. Thus, the present study utilized ecological momentary assessment (EMA) to examine the effects of daily deviations in total sleep time (TST) and person-average TST on anxiety and whether these effects varied as a function of time of day in a sample of unselected adults (N = 138). Results indicate that the amount of TST on a given night, relative to personal average TST, negatively predicted anxiety, and this relation was significant in the morning and afternoon, but not evening. In contrast, person-average TST was unrelated to average anxiety. Relations between TST and anxiety did not differ across objective (e.g., actigraphy) and subjective (e.g., sleep diary) measures. Furthermore, the pattern of results remained the same when controlling for previous day's anxiety and were not bidirectional. These findings suggest that getting less sleep than is typical for the individual predicts subsequent anxiety, and this effect is particularly strong in the morning. Average sleep duration may be less important to the experience of anxiety than deviations from that average. These findings highlight the importance of EMA to examine how and when variability in sleep confers vulnerability for anxiety symptoms.

It's craving time: time of day effects on momentary hunger and food craving in daily life

A key determinant of food intake besides hunger is food craving, which refers to an intense desire to consume a specific food. Although they commonly co-occur, they are conceptually different and their dissociation is thought to underlie unhealthy eating (e.g., eating in the absence of hunger). To date, we know almost nothing about their coherence (or dissociation) in daily life or about the role of time of day and different food types. The present investigation assessed both hunger and food craving for several food categories in daily life using smartphone-based ecological momentary assessment. Across three independent studies (n = 50, n = 51, and n = 59), participants received five or six prompts a day and reported their momentary hunger and desire for tasty food (a subcomponent of food craving). Consistent across studies, hunger and desire for tasty food exhibited largely similar patterns throughout the day with two peaks (roughly corresponding to lunch and dinner). Examining more specific food categories, study 3 found that although desire for main meal-type foods had a two-peak pattern in coherence with hunger, this pattern was different for snack-type foods: Desire for fruits decreased, whereas desire for sweets and salty snacks increased throughout the day with less coherence with hunger. These findings suggest that dissociations between hunger and craving are found only for snack-type foods, whereas hunger and general food cravings cohere strongly. Interventions addressing snacking may take these circadian patterns of food cravings into account.

It's craving time: Time of day effects on momentary hunger and food craving in daily life

It's craving time: Time of day effects on momentary hunger and food craving in daily life

Effects of time of day on age-related associative deficits.

Time of day is known to influence cognition differently across age groups, with young adults performing better later than earlier in the day and older adults showing the opposite pattern. Thus age-related deficits can be smaller when testing occurs in the morning compared with the afternoon/evening, particularly for tasks requiring executive/controlled/inhibitory processes. Stronger influences of time of day were therefore predicted on associative than on item recognition memory based on their differential requirements for demanding recollective (rather than familiarity) processes. In 2 experiments, participants were presented with unrelated word pairs and then tested on both item recognition (old/new item?) and associative recognition (intact/recombined pair?). In Experiment 1, young adults were tested either in the morning or in the evening; recognition memory was better when time of testing matched participants' morningness-eveningness preferences, and more so for associative than for item memory. In Experiment 2, young and older adults (evening and morning types, respectively) were tested both in the morning and in the evening; again, recognition memory was better at participants' preferred times of day, especially for associative memory. Consequently, age-related associative deficits varied considerably-indeed more than fourfold-from a nonsignificant 8% for testing in the morning to a substantial 35% for testing in the evening, suggesting that it is important to consider time of day effects in future studies of the associative deficit hypothesis. (PsycINFO Database Record