The manner in which human faces are perceived is very strongly influenced by their orientation although inverted photographs of faces remain difficult to recognize mainly because they lose their expressive distinctiveness hence becoming impossible to categorize them. According to Literature, the important features which are used to distinguish faces are normally represented in memory with respect to the normal upright posture; hence an inverted face must be positioned mentally upright before it can be recognized.
It could also be difficult to reorient stimuli which have multiple parts and more especially hard to recognize inverted stimuli in which the distinguishing features involve relations among adjacent contours. Therefore, the fact that the recognition of human faces is more susceptible to stimulus inversion than is recognition of any other group of stimuli has been considered as evidence that faces are a special stimuli.
Empirical evidence in standard behavioral paradigms show that faces are recognized using a different method of computation from objects. Though the difference is not precisely understood, its established that if compared to other objects the processing for faces involves a much stronger and mandatory perceptual integration (Riddoch, 2008).
Face perception fundamentally is the process by which the brain and the mind comprehend and understand the face and more predominantly the human face. From the time an individual is born, the face is necessary for social interaction and face perceptions are very sophisticated because the facial expressions involve quite a number of areas in the brain. In addition, if some parts of the brain are impaired; it leads to misunderstanding of faces. The proportions and expressions of the human face are essential in identifying the origin, mental tendencies, health qualities and some collective information.
According to past research on infants perception of faces, its a fact that faces are important stimuli for infants. This is because they see faces very often and use them to help identify and interact with others as well as learn more about the world. However, an issue of concern in this study is whether the infants perceive the faces as something special or they view them in the same way that they look at other complex objects. In most instances, people have always argued out that faces are a unique class of objects and that infants process faces in a different way from the manner in which newborns process non-face stimuli.
One of the most common and widely recognized face perception theories implicate that there are several processes that are involved in understanding faces right from the fundamental perceptual management on the sensory information to obtain particulars about a person, to being able to remember significant specific information like their name and any pertinent past experience (Zhao, 2003).
A model developed by Vicki Bruce, a psychologist, argues out that the concept of face perception may involve a variety of sub-independent processes which work together to accomplish a common goal. This model goes ahead to describe the process of face perception as follows. There is a derivation of a view-centered description from the perceptual input whereby simple aspects of the face are used to work out details like age, gender and other basic facial expressions.
This initial information is then used to create a structural model of the face that allows it to be measured up to other faces in reminiscence. This is the reason as to why if a person is viewed from different angles, he can still be recognized hence this structural programming can be considered to be specific for upright faces. Additionally, this kind of programming is transferred to notional face recognition units which are then used with the personal identity nodes to recognize a person through information obtained from the semantic memory (Young, 1992).
Recent models of face recognition emphasize the necessity of separating stimulus recognition from face recognition. Putting in consideration the natural daily life conditions and the perceived dimensional representations, it looks like a face-recognition process may be evaluated at times when only the stimulus responsible of recognizing differs from the stimulus that had been previously stored in the memory. In such a case, the subject at hand has to give detailed information of the face. This should be independent of the direction and appearance of the really alleged stimulus (Young, 1992).
Faces are believed to be made up of a broadly and uniquely used group of stimuli and despite their importance; there are a few collections of faces that are used in research. However, none of these faces sufficiently represent the different ages of faces across the natural life. As a result, the lack of a variety of ages has therefore limited the majority of researchers. Hence they are restricted to using young faces as stimuli even when their research dictates that they use both young and old participants (Park, 2004).
Recent surveys of psychological literature indicate that over 200 research studies have previously been conducted with using images of faces as stimuli. These studies were intensive and they covered broad areas that included discernment, concentration, reminiscence, social reasoning and sentiments. Results from this studies concluded that faces are a distinctive category of objects because all people with sight have an experience with them and they still find it hard to express them.
There are so many arguments about faces being unique stimuli; there is much evidence in support which reveals that faces unlike other visual objects are uniquely processed in specific sites in the fusiform gyrus. This implies that certain neuroanatomical sites are specialized for processing faces with identical configuration details. Therefore, when differences are found in memory for meaningful pictures in old and young individuals, there occurs a behavioral separation between facial memory and memory from other complex objects (Park, 2004).
As much as it is hard to agree on the arguments about the existence of face specific neural mechanisms, its equally difficult to establish the processes that might distinguish the recognition of faces from those of other objects. A common assumption is that the recognition of objects is analytic and part-based while that of face-recognition is holistic and configural. Past researchers findings that face inversion damages the identification of faces more than other objects support this assumption.
This is because inversion damages the perception of the spatial configuration among features on which face acknowledgment depends more than recognition of the features (Kanwisher, 2000).
The fusiform face area is a face selective region in the human extrastriate cortex. However its function still remains an issue of debate. A correlation of the fusiform face (FFA) area activity and the magnetic resonance imaging was measured against the behavioural outcomes in perceptual tasks to determine the role of the FFA in the detection of faces and objects.
Data reveals that FFA activation is connected with both face and object detection although most non-face object identification as correlated to activation in other areas of the ventral occipitotemporal cortex. Hence, these findings imply that the FFA is involved in both detection and identification of faces though it is minimally involved in recognition of non-face objects.
Activation of the FFA in the human extrastriate cortex occurs twice and s activated twice as strongly when people view faces as compared to when they look at other types of objects. Prior experiments indicate that the activation of FFA is connected to the perception of the face in binocular rivalry, the face and imagery of the face. However, some researchers have suggested that the essential information about faces lies exteriorly to the FFA and that it may also be engaged in the interior category identification of non-face objects (Druzgal, 2001). The FFA is assumed to be performing the following functions:
(a) Detection of the presence of faces
(b) Recognition of specific faces
(c) Differentiation of stimuli from any other form of object
(d) Identification of stimuli from categories for which the subject gain expertise (Druzgal, 2001)
In order to assess the neural associates of recognition and identification, a brief masked stimulus was presented in a rapid event- related MRI design and afterwards compared to the blood oxygenation level-dependent signal on trials where subjects failed to recognize stimuli. In each of the experiments, the subjects perceived images from one category.
Half of the objects contained different images of specific category target and the rest were different from the same category. These tests enhanced the comparison of the size of response in the FFA when subjects correctly identified the target (Knouf & Kanwisher, 2004).Previous MRI results show that extrastriate visual areas have predominant functions in the perceptual processing while the prefrontal cortex serves a predominant role in working memory (Baseler, 1997).
Baseler, H. (1997). Extrastriate visual signals. Cerebral cortex. Vol.7(1):181-192
Druzgal, T. (2001).Activity in fusiform face area. Retrieved on August 2, 2010 from http://www.ncbi.nlm.nih.gov/pubmed/11167061
Kanwisher, N. (2000). The cognitive neuroscience of face processing. Cognitive neuropsychology. Volume 17(2):1-11
Knouf, N & Kanwisher, N. (2004). The fusiform face area. Nature neuroscience.Volume 7(1):555-562
Lerner, R.(2003). Handbook of psychology: Developmental psychology. New Jersey: John Wiley & Sons.
Park, D. (2004). A lifespan database of adult facial stimuli. Behavioral research methods, instruments and computers. Volume 36(4):630-633
Riddoch, M. (2008). Cognitive neuropsychology. Behavioral brain sciences. Volume 25(5): 765-8