An emotional bias is a distortion in cognition

Cognition

In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...

 and decision making

Decision making

Decision making can be regarded as the mental processes resulting in the selection of a course of action among several alternative scenarios. Every decision making process produces a final choice. The output can be an action or an opinion of choice.- Overview :Human performance in decision terms...

 due to emotional factors.

That is, a person will be usually inclined

• to believe something that has a positive emotional effect, that gives a pleasant feeling
  Feeling
  Feeling is the nominalization of the verb to feel. The word was first used in the English language to describe the physical sensation of touch through either experience or perception. The word is also used to describe experiences, other than the physical sensation of touch, such as "a feeling of...
  
  , even if there is evidence to the contrary.
• to be reluctant to accept hard facts that are unpleasant and gives mental suffering
  Suffering
  Suffering, or pain in a broad sense, is an individual's basic affective experience of unpleasantness and aversion associated with harm or threat of harm. Suffering may be qualified as physical or mental. It may come in all degrees of intensity, from mild to intolerable. Factors of duration and...
  
  .

Those factors can be either individual and self-centered, or linked to interpersonal relationship

Interpersonal relationship

An interpersonal relationship is an association between two or more people that may range from fleeting to enduring. This association may be based on limerence, love, solidarity, regular business interactions, or some other type of social commitment. Interpersonal relationships are formed in the...

 or to group influence

Group-serving bias

Group-serving bias is identical to self-serving bias except that it takes place between groups rather than individuals, under which group members make dispositional attributions for their group's successes and situational attributions for group failures, and vice versa for outsider groups.For...

.

The effects of emotional biases

Its effects can be similar to those of a cognitive bias

Cognitive bias

A cognitive bias is a pattern of deviation in judgment that occurs in particular situations. Implicit in the concept of a "pattern of deviation" is a standard of comparison; this may be the judgment of people outside those particular situations, or may be a set of independently verifiable...

, it can even be considered as a subcategory of such biases. The specificity is that the cause lies in one's desires or fear

Fear

Fear is a distressing negative sensation induced by a perceived threat. It is a basic survival mechanism occurring in response to a specific stimulus, such as pain or the threat of danger...

s, which divert the attention of the person, more than in one's reasoning.

Neuroscience

Neuroscience

Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...

 experiments have shown how emotions and cognition, which are present in different areas of the human brain, interfere with each other in decision making process, resulting often in a primacy of emotion

Emotion

Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...

s over reasoning http://ccat.sas.upenn.edu/bmcr/2004/2004-04-19.html

Emotional bias might, for example, help explain the tendency towards over-optimism

Optimism

The Oxford English Dictionary defines optimism as having "hopefulness and confidence about the future or successful outcome of something; a tendency to take a favourable or hopeful view." The word is originally derived from the Latin optimum, meaning "best." Being optimistic, in the typical sense...

 or over-pessimism

Pessimism

Pessimism, from the Latin word pessimus , is a state of mind in which one perceives life negatively. Value judgments may vary dramatically between individuals, even when judgments of fact are undisputed. The most common example of this phenomenon is the "Is the glass half empty or half full?"...

, even when evidence for a more rational conclusion is available.