Early in the development of psychology, an observation was made: human beings differ from one another. They differ in the way they react to certain environments, in the way they communicate with other people, in the way they absorb knowledges, and so on. This observation led to the factor theory of human behavior - the idea that certain definable factors underlie human behavior. Psychologists developed a field called psychometrics to answer the question of (1) what are the major factors and (2) how can they best be measured? The basis of psychometrics is the measurement of individual differences in mental abilities or traits through the evaluation of a representative sample of behavioral products in a standardized situation. It has given rise to a diversity of theories, all of which, however, share a belief that the test scores are meaningful numbers that can be manipulated mathematically to gain psychological insights. They share also an underlying assumption that human variability exists in all traits, the scores on which when measured are assumed to be distributed approximately normally. According to the psychometric measures of ability, we can assume that there exist individual differences among human beings. But psychometrician only proved that there were individual differences. What cause individual differences? How can we explain these phenomena? Psychometrician did not give clear explanation to these questions about individual differences. Cronbach (1957) pointed out that two mainstreams of scientific psychology flowed without recognizing their counterparts. One is the psychometric approach which only interested in measuring individual differences without focusing on problem solving human beings face. Another is the experimental psychology which study general cognitive processes without understanding individual differences. We think two mainstreams should be jointed to study further human abilities. Most cognitive psychologists have a generally accepted view that human intelligence reflects both sides; a person's knowledge of the world and some basic set of skills for processing information. With the recent interest in human intelligence, a lot of efforts have been directed toward isolating these basic information processing skills and determining the extent of their relationship to traditional psychometric measure of ability. This study is an attempt to discover the relationships between information processing parameters and measures of ability (Spatial Ability). This approach is called cognitive-correlates theory. 580 subjects (students at Y high school in Seoul) were tested by a spatial ability test. It was developed by editing and classifying the items which measure spatial ability from various kinds of ability tests. The obtained data from the spatial ability test were almost normally distributed. We selected 40 subjects with the application of random sampling method; half from upper quartile (Spatial Ability High Group) and half from low quartile (Spatial Ability Low Group). The 40 subjects were asked to respond to questions given by Apple Ⅱ computer. The experiment-programs are presented in the appendix. Major variables were "Holding capacity of short-term memory", "Manipulation of information in short-term memory", "Searching skill of long-term memory", and "Organization of information in long-term memory". Major finding were as follows ; 1. In Holding capacity of short-term memory, two groups showed significant difference. High group students used syllabizing strategy in memorizing given letters, while low group students did desultory one. 2. In Manipulation of information in short-term memory, two groups disclosed significant difference. This indicated operation skill of high group was different from that of low group. 3. In Searching skill of long-term memory, two groups represented significant difference. High group students performed the task by imagining a specific part of one object in the pair rotated into the orientation of the other object and then comparing the transformed internal representation with the second object to determine whether there was a match or mismatch in shape, while low group ones did not. 4. In Organization of information in long-term memory, two groups indicated significant difference. High group students used link strategy that vertex number of given figure was matched to the internal representation of given figure, while low group ones matched internal representation of given figure to the angle of given figure.