Extended Abstract
1. Introduction
Marital satisfaction is defined as the individuals’ satisfaction with their marital life. New evidence suggests the effective role of physiological, cognitive, and emotional factors in the quality of the relationship between couples. One of the biological variables that can affect couples’ compatibility is sleep-wake cycle and one of the most important individual differences is morningness-eveningness personality.
Evidence shows that morning people obtain higher scores in memory and attention. Morningness is positively related to life satisfaction and quality of life. On the other hand, eveningness is positively associated with depression, low sleep quality, undesirable personality profile, and health-damaging behaviors. Based on what was discussed, morningness-eveningness preferences can partly predict personality type, quality of life and life satisfaction and thus marital satisfaction. Another variable that may be related to the rate of marital satisfaction is couples’ cognitive function. Cognitive flexibility is one of the most fundamental dimensions of cognitive functions and is among the most important elements of executive functions, applied to the individual’s ability to change thoughts, actions, and strategies in response to changes in circumstances. Flexible cognition requires the activation and modification of cognitive processes in response to calls for changes in doing an activity or even changes in the instruction for doing an activity.
People with the ability to think flexibly use alternative justifications, positively rebuild their intellectual framework, accept challenging situations or stressful events and are psychologically more resilient compared to those who have less flexibility. In addition to physiological and cognitive variables, one of the most important deficiencies that has a profound effect on the quality of communication patterns of individuals includes emotion regulation strategies. Since psychological adjustment largely depends on emotion regulation, this ability can affect couples’ marital satisfaction. The present study aims to investigate the relationship between morningness-eveningness personality, cognitive flexibility and cognitive emotion regulation with marital satisfaction in married middle-aged women.

2. Method
The current study was a correlational research. The statistical population comprised all married middle-aged women (40-60 years old) living in Mashhad City, Iran. District 1 was randomly selected as the sample area and from this district, 211 women were chosen through systematic sampling method. The research inclusion criteria consisted of the following: female gender, age between 40 and 60 years, living in Mashhad at least for the past two years and having at least a diploma.
The exclusion criteria were as follows: widows and divorced people, complete cessation of sexual relationship with the spouse, having extramarital relationships, having serious suicidal thoughts, having a history of admission to psychiatric hospital, suffering from the symptoms of psychotic disorders and drug addiction. The participants completed enrich marital satisfaction scale, cognitive flexibility inventory, morningness-eveningness questionnaire and short form of cognitive emotion regulation questionnaire. The obtained data were analyzed using Pearson correlation test and multivariate regression analysis.

3. Results
The relationship between psychological flexibility and marital satisfaction (r=0.26) and the relationship between all the subscales of cognitive flexibility and marital satisfaction were significant and positive (P<0.05). Multivariate regression results revealed that the subscales of perception of alternative options, perception of controllability, and total score of cognitive flexibility are able to positively predict marital satisfaction (P<0.05). Moreover, the role of morningness-eveningness personality was significant in predicting marital satisfaction, and high morningness was associated with high marital satisfaction (r=42, P<0.01). Additionally, the results about emotion regulation components demonstrated that self-blame, rumination, catastrophizing and blame of others negatively predict marital satisfaction, and acceptance and perspective-taking positively predict marital satisfaction (P<0.05).

4. Discussion
Results of the present study indicate a significant and positive relationship between marital satisfaction and psychological flexibility. Cognitive flexibility is one of the dimensions of executive functions which refers to the ability to change the actions and thoughts in accordance with environmental demands. In other words, when a person uses cognitive strategies to change behavior and adapt to the environment, he enjoys flexible cognition. The relationship between couples also includes various complex and challenging situations which require the use of a flexible cognitive pattern.
In the event of conflicts and disagreements, successful couples benefit from negotiation and effective emotional and cognitive strategies. These strategies, while ending the conflicts and disagreements, bring couples emotionally closer together and cause them to better perceive each other’s support. Accordingly, high cognitive flexibility is expected to be accompanied by marital satisfaction. Morning people compared to evening people are more optimistic and are emotionally stable, serious, and reliable. Morningness personality enjoys more cognitive processes, leading to more adaptation and adjustment with the environment.
All of these facts, therefore, lead to greater satisfaction with relationships, especially the relationships between couples. Cognitive emotion regulation is applied with the purpose of emotion management to increase adjustment and compatibility and is part of adaptation strategies that are associated with experience and treatment of emotional and physical discomfort. Accordingly, it is expected that high capability in cognitive emotion regulation lead to greater marital adjustment between couples and consequently increased satisfaction.
Cognitive emotion regulation plays a fundamental role in various normal and abnormal processes and is one of the important components of the coping process against negative stimuli and unpleasant emotional experiences. Therefore, low emotion regulation skill is associated with poor coping and thus experience of negative emotions and these emotions affect the quality of the relationship between couples and can reduce marital satisfaction. With regard to the use of a correlational design in this study, marital satisfaction cannot simply and certainly be affected by just predictor variables in this study. Another limitation of the present study was the research sample (married women of District 1 in Mashhad). It is suggested that empirical designs and larger samples be used in future research.
Findings of the present research, while expanding the research literature, highlight the necessity of considering physiological, cognitive and emotional characteristics in programs for the promotion of the relationships between couples and premarital counseling.

Ethical Considerations
Compliance with ethical guidelines
In order to observe ethical issues, after the participants’ awareness of the goals and process of the research implementation, written consent was obtained from all participants and they were assured that the received information would remain completely confidential. This study has been conducted with the approval of the Research Deputy of Neyshabour Islamic Azad University.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors contributions
The authors contributions is as follows: Conceptualization: Hossein Shareh, Maryam Eshaghi Sani; Research and investigation: Hossein Shareh, Maryam Eshaghi Sani; Edition and finalization of the text: Hossein Shareh; Resources: Hossein Shareh, Maryam Eshaghi Sani; and Project monitoring and management: Hossein Shareh.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgements
Hereby, we offer our thanks to the respectable officials of Mashhad Municipality and the chief and staff of Rahyab Specialized Counseling Center for Mental Disorders and Sexual Dysfunctions in Mashhad, who assisted us in doing this research.