## 1 Introduction
### The Spatial Skills and the Spatial Perception  
Spatial skills have been the subject of extensive research for more than a century and are an important line of research in cognitive and educational psychology. Researchers in the field of human intelligence agree that our intelligence is not unique and that it consists of several different components. All the theories and studies carried out in this field concur that one of the components of intelligence is directly related to our visual and spatial capacities as they function within the mental representation of two- and three-dimensional spaces, as well as facilitate the resolution of spatial problems, whether real or imaginary. Spatial skill is a component of human intelligence. It is understood as the ability to generate, retain, retrieve, and transform well-structured visual images [8]. However, as seen in the definition itself, there is no clear agreement about the subskills or components that shape this ability [9]. For example, [PERSON] [10] distinguishes five components of spatial skills: spatial perception, spatial visualization, mental rotation, mental relationships, and spatial orientation. Recent research such as the Cattell-Horn-Carroll Model of Intelligence [11] shows eleven spatial skills that constitute Spatial Cognition, while even more recent studies, based on the previous model and new contemporary theories, conceptualize the Spatial Cognition or Visual Processing consisting of 25 factors [12]. Many of these factors are interrelated yet psychometrically measurable, thus rendering them highly important as they relate to university educational success. Some researchers, like [PERSON] [13], recognize only two components: spatial visualization, understood as the ability to mentally handle complex forms, and mental rotation, defined as the mental speed to rotate simple forms and recognize them whilst in another position. The simplification of the components of spatial skills responds in general to the relationship that researchers seek with the possibility of training these skills in the field of engineering, and looks to generate a positive impact [14]. For the methodological and practical effects of this research we will consider the two components proposed by both [PERSON] [15] and supported by [PERSON] [16]: spatial visualization and spatial orientation. The spatial visualization component entails mentally moving an object, whereas the spatial orientation component requires the ability to mentally move a given viewpoint while the object remains fixed in space. The spatial visualization component is subdivided in two categories, Mental Rotation and Mental Transformation, the difference being that with Mental Rotation, the whole object is transformed by rotating it in a given space, while with Mental Transformation, only a specific part of the object undergoes some kind of transformation (Figure 1). We consider that this scheme is better adapted for the research concerning the exploration of architectural spaces. This is due to the fact that the objects that must be mentally manipulated and understood are objects or spaces in which the user can enter and even (mentally) travel through, thus obtaining perceptions or sensations within them as opposed to other objects in which the observer does not have that possibility. On the other hand, the perception of extrapersonal space, or simply spatial perception, involves not one but many specific skills. For example, within the visual domain, they include locating points in space, determining the orientation of lines and objects, evaluating the location in depth, observing the geometric relationships between objects and processing movement among many others [17].