One can get quite confused when talking about basic terms in meditation, such as "awareness", or "mindfulness".
One has to know the context in which terms are used. For the term "awareness", one must distinguish the biological, brain-based meaning from the Buddhist metaphysical meaning relevant for meditation.
As a novice do-it-yourself meditator, I first encountered the term 'awareness' through the late meditation teacher Culadasa (John Yates, author of The Mind Illuminated). Culadasa was deeply steeped in Buddhism and a cognitive scientist who interpreted classical meditation terms through the lens of neuroscience.
Here, awareness is a function of the brain working in conjunction with focused attention. It is a mode of perception.
Then, through the late meditation teacher Daniel P Brown, author of Pointing Out the Great Way, I was introduced to Mahamudra and Dzogchen.
Here awareness is not a biological concept. It is a metaphysical concept. Awareness is completely independent of the brain. It is not a cognitive function, but the "ground" of consciousness and perception, the "space" in which all mental events occur.
Awareness from a cognitive science point of view
From a cognitive science point of view, "awareness" (as "peripheral awareness") is a specific mode of perception. It is complementary to attention (as "focused attention"). It is based on its own set of circuits.
Narrow (but variable)
Sense of Self
Holds potential objects of awareness
Selects objects from awareness, bringing them into full consciousness
Fast (near immediate)
Slow (200 milliseconds)
Awareness from a Tibetan Buddhism point of view (Rigpa)
In Tibetan Buddhism, awareness is not a cognitive and brain-based function or capability. Instead, it denotes something like this:
A self-less, boundaryless, timeless, propertyless, luminous field of knowing, in which all mental events appear. "Mental events" includes all types of what´s called experience: sensations, thoughts, emotions, the sense of Self, the sense of having a body etc etc.
This field of knowing awareness is also called "the natural state". The meditator is trained to "become" this awareness field, instead of operating from the point of view of a localised self looking out of the eyes.
This field of knowing awareness is called "rigpa" in Tibetan. This concept of awareness is not a scientific explanation. Instead, it is a description that is in accord with meditative practice and the metaphysical / ontological foundations of Tibetan Buddhism
Thus, in this concept of awareness, it would be wrong to say that awareness has a speed, a function, or a focus. Such properties would be ascribed to the mind and its biological functioning.
From the point of view of cognitive science, what are the differences between attention and awareness
What are the differences in meaning of the term awareness between cognitive science and Tibetan Buddhism
Austin, J. H. (2013). Meditating Selflessly: Practical Neural Zen (Mit Press) (Illustrated). The MIT Press. https://www.amazon.com/Meditating-Selflessly-Practical-Neural-Press/dp/0262015870
Brown, D. P., & Thurman, R. (2006). Pointing Out the Great Way: The Stages of Meditation in the Mahamudra Tradition (Annotated). Wisdom Publications.
https://www.amazon.com/Pointing-Out-Great-Way-Meditation/dp/0861713044 The book builds on the 1981 dissertation by Daniel P Brown "Mahamudra Meditation Stages". This text is discussion topic on a "conscious.tv" series https://www.youtube.com/watch?v=grBkn9fWD6Y
Yates (Culadasa), J., & Immergut, M. (2017). The Mind Illuminated: A Complete Meditation Guide Integrating Buddhist Wisdom and Brain Science for Greater Mindfulness. Hay House Uk. https://www.amazon.com/Mind-Illuminated-Meditation-Integrating-Mindfulness/dp/1781808201