A short history of attention:
Human attention is an obvious phenomenon which is active during every single moment of awareness. It was studied first in philosophy, followed by experimental psychology, cognitive psychology, cognitive neuroscience and finally computer science for modeling. Those studies are not a serial experience, but they add the one to the others as the layers of an “attention onion” (Figure 1).
Due to the high diversity of applications of attention, a precise and general definition is not easy to find. Moreover, the views on attention evolved in time and research domains. In this first part of an attempt to get a definition of attention, we go through a brief history on the related research from philosophy to cognitive psychology. This first part addresses the times where the study of attention was more or less included in one single community.
Conceptual findings: attention in philosophy
A first important study on human attention was the one of N. Malebranche, a French oratorian priest who was also a philosopher. In his “The search after truth” published in 1675, Malebranche focused on the role of attention as a structuring system in scene understanding and though organization.
In the 18th century, G. W. Leibniz introduced the concept of “apperception” which refers to the fact of assimilating new and past experience into a new view of the world . Leibniz intuition is about an involuntary approach to attention (known today as a “bottom-up”) which is needed for a perceived event to become conscious.
In the 19th century, Sir W. Hamilton, a Scottish metaphysician, changed the previous view on attention which consisted in thinking that humans can only focus on a single stimulus at once. Hamilton noted that when people throw marbles, the placement of only about seven of the marbles could be remembered . This finding opened the way to the notion of “divided attention” and led about one century later to the famous paper of G.A. Miller, “The Magical Number Seven, Plus or Minus Two” in 1956 .
Attention in experimental psychology
After the first philosophical approaches, attention entered in a scientific phase when approached by psychology. Based on an observation error detected in astronomy, W. Wundt introduced the study of consciousness and attention to the field of psychology . He interpreted this observation error as the time needed to switch voluntarily one’s attention from one stimulus to another and initiated a series of studies on the mental processing speed as the ones achieved by F. Donders .
At the second half of the 19th century, H. Von Helmholtz, in his “Treatise on Physiological Optics”  noted that despite the illusion that we see all our environment in the same resolution, humans need to move their eyes around the whole visual field “because that is the only way we can see as distinctly as possible all the individual parts of the field in turn.” Even if he personally mainly inspected the eye movement scanpath (overt attention), he also treated on the existence of a covert attention (which does not induce eye movements). Von Helmholtz focused on the role of attention as an answer to the question “Where” the objects of interest are.
In 1890, W. James, published his textbook “The principles of psychology”  and remarked that attention is closely related to consciousness and structure. According to James, attention makes people perceive, conceive, distinguish, remember, and shorten reactions time. James indeed linked attention to the notion of data compression and memory. Contrary to Von Helmholtz, James is more focused on the fact that attention should answer to the question of “What” are the objects of interest.
Attention in cognitive psychology
Between the very beginning of the 20th century and 1949, the mainstream approach in psychology was the behaviorism. During this period, the study of mind was considered as barely scientific and no important advances were achieved in the field of attention. Despite this “hole” in the study of attention we can still find names as J. R. Stroop who worked on the “Stroop Effect”  showing that divergent stimuli (reading/color) heavily impair people performance.
After the Second World War and its practical questions on soldiers’ attention and the development of the cognitivism, the study of attention made a tremendous comeback. To the behaviorist view which states that the organism behavior is under environmental control, the cognitivism showed that behavior can be modulated by attention.
The come-back of attention begun with the work of C. Cherry in 1953 on the famous “cocktail party” paradigm . This approach models how do people select the conversation that they are listening to and ignore the rest? This problem was called “focused attention”, as opposed to “divided attention”.
- Broadbent  summarized most of the findings known until then in a “bottleneck” model in which he described the selection properties of attention. The idea is that attention acts like a filter (selector) of relevant information based on basic features, such as color or orientation. If the incoming information matches the filter it can reach awareness (conscious state), otherwise it will be discarded. At that time, the study of attention seemed to become very coherent and was called “early selection”. Nevertheless, after this short positive period, most of the findings summarized by Broadbent proved to be conflicting.
The first “attack” came from the alternative model of Deutsch and Deutsch  who used some properties of the cocktail-party paradigm to introduce a “late selection” model, where the attentional selection is basically a matter of memory processing and response-selection. The idea is that all information is acquired, but is selected to reach awareness only the one which fits semantic or memory-related objects. This is an opposite view to Broadbent who professes an early selection of the features before they reach any further processing.
New models were introduced like the attenuated filter-model of A. Treisman  which is a softer version than Broadbent bottleneck and which let stimuli with a response higher than a given threshold switch the filter, thus the focus of the selective attention.
Later, in 1980, Treisman and Gelade  proposed a new “feature integration” theory, where attention occurs in two distinct steps: a preattentive parallel effortless step which analyze objects and extracts features from those objects. In a second step, those features are combined to obtain a hierarchy of focus attention which pushes information towards awareness.
Despite its high importance within the psychology theories, the feature integration was also highly disputed. Other theories emerged as M. Posner  spotlight supporting a spatial selection approach or D. Kahneman  and his theory of capacity supporting the idea of mental effort.
In the late 1980s, a bunch of theories on attention flourished and none of them was capable of including all previous findings. According to H. Pashler , cognitive psychology reached a dead-end. After several decades of research in cognitive psychology, more questions were raised than answers given. Pashler declared that “No one knows what attention is” as a provocative response to the famous “Everyone knows what attention is” proposed by James one century before.
The need for new approaches: after the late 1980s “crisis”
Attention deals with the allocation of cognitive resources to important incoming information in order to bring them to a conscious state, update the scene model and memory and influence behavior. Between consciousness, memory and behavior, attention revealed to be much more complex that initially expected and some people even question the fact that attention is one single concept or there are several “attentions”. Sometimes, attention became a kind of magical box where everything which could not be explained otherwise can get.
The number of issues and the complexity of the nature of attention led to an interesting move in the split of attention study from one single community into two different communities.
One has a will of getting further into the theoretical and the profound nature of attention (cognitive neuroscience) using adapted simple stimuli. The arrival of advanced tools such as functional imaging or single-cell recordings will allow them to make huge steps towards attention understanding.
The second community working in the attention field has a will of making the concept work with real data such as images, videos or others (computer science). From the late 1990s and the first computational models of visual attention those two approaches developed in parallel, one trying to get more insight on the biological brain and the other trying to get results which can predict eye behavior for real-life stimuli. Even if the computational attention community led to some models very different from what is known to happen in the brain, the engineers’ creativity is impressive and the results on real-life data begin to be significant and the applications endless.
In a second part of our attempt to know more about what attention is, we will focus on cognitive neuroscience on one side and on computational attention on the other along with the known properties of attention.
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