The simple and almost trivial argument of this talk can be summarized like this.
-Human-computer interaction (HCI) is a human action making use of computers (which means, making use of machinery called software).
-This action involves operations carried out by the computer. They appear to us as if the computer was also active (which in a way, it is).
-The human and the computer are constantly taking turns in their action and operation and, therefore, we call this entire happening "interaction".
-Since interactive use of the computer by necessity requires sensory perception and, consequentially, interpretation, aesthetics must play an important role. This is so if we consider aesthetics as the study of sensory perception and understanding.
Nothing in the world is true nor good nor beautiful. It is only through human judgment that layers of truth or goodness or beauty are generated. This is by three kinds of judgments: the logic, the ethic, and the aesthetic kind of judgment. So aesthetrics is, first of all, a way of making judgments. In so far, it is relational. It is not about features and properties of things.
The aesthetic judgment discriminates at the sensory level but it possesses the innate tendency of going beyond the sensory domain. So in the aesthetic judgment, we have discrimination and valuation. Valuation is definitely different from evaluation: it is about qualities, whereas evaluation may result in quantity and, in fact, much research aims at this.
The subject matter of aesthetics before valuation thus appears as human sensory perception as a component of semiosis, i.e. as the start into a sign process: a process of interpretation and re-interpretation, essentially without end. Visual aesthetics has ist subject matter reduced to the visual case.
Until recently, usability was a great concern within the HCI community. It is not possible to seriously compare aesthetics to usability unless we destroy aesthetics to some sort of instrument. It may, however be justified to identify a few features of usability vs. Aesthetics. To usability, the computer is like a tool; only in an environment of work activity does usability make sense; here we have tasks and immediate purposes and, therefore, prediction and measure; in general, usability is a matter of practical reason.
To aesthetics, the computer is like a medium; it becomes important in game activities; decision making and values are guiding principles; and aestheics is a matter of contemplative reason.
As a general concept, I want to remind of software objects as algorithmic signs. These are signs that allow for, and require two interpretants: the intentional and the causal interpretant. Algorithmic signs are perceivable (by us) and computable (by the computer). They connect the aesthetic with the algorithmic domain. They have, metaphorically speaking, a surface and a subface.
As a radically agnostic position, I view the world as the world and nothing else. It is the whole that some call "god". We can have it in parts only. From a particular (sic!) perspective, the aesthetic perspective, e.g., the world appears as aesthetic signs, aesthetic processes, and aesthetic judgments. Since the aesthetic perspective is the perspective of perception, HCI has no choice but turn to aesthetics in its attempt to better understand certain processes.
HCI, in my view, is the weak coupling of two semiotic processes, one of them a full-fledged sign process (on behalf of the human), the other one reduced to a signal process (on behalf of the computer). Therefore, the (visual) aesthetics of HCI is the aesthetics of algorithmic signs as they appear in environments of interaction.
Questions of HCI must be tackled from here, i.e. from the dialectics of the newly discovered sign class, the algorithmic sign. The designer can manipulate the subface of the algorithmic sign. He has no influence on the surface except for the most trivial projection to the display screen. He can, however, make great use of the algorithmic side of the algorithmic sign.
This new challenge for aesthetics is what HCI is about. It may be the case that my plea for a radical aesthetic turn in HCI is off the main orientation of experimental psychology as a kind of normal science (Thomas Kuhn) exploring quantitatively what aesthetics may have to offer. In that case I apologize for an intervention whose basis is design more than analysis.