Perceiving and Representing Our Dynamic World
In many ways the film industry has provided us with great insight into understanding how humans perceive motion. Similarly, the contrary also holds true: understanding the intricacies of our eyes and how we see has enabled film-makers to replicate the experience of motion to a scaringly high degree of accuracy.
Benjamin Franklin once said, “Never confuse motion with action”. Although he may have meant this in a different context, taking its literal meaning also holds true from a psychological perspective. Just because we perceive motion, it does not necessarily mean there is action in our environment. Our predisposition to consider the two elements interchangeably is largely due to the neuronal processes that occur in our brain. But what is motion in the first place? Physically we can describe it as the change in position (from a point of reference) over a given amount of time. Yet sometimes we perceive motion in relatively static objects. In this respect, we can describe motion simply as a human percept- something we can see and communicate. Moving image makers have exploited this aspect of motion in the making of movies. We do not simply see motion; we imagine and create it also.
The perception of motion involves a hierarchical process, much like the perception of colour or form. In its first order, sensation is stimulated by the sequential excitation of photoreceptors on the retina by a series of photons. The second order is heavily based on the cues from salient features extracted through early vision, such as distinctive colour, texture, flicker or contour (Vaina, L. M., & Cowey, A. (1996)). These separate perceptual pathways only intersect in the visual cortex (specifically the V5/MT region), where they are integrated into what we perceive as coherent motion. Yet, it must be noted that processing in the visual cortex depends solely on what we detect in these sensory pathways. Thus we are unable to distinguish between whether we are really seeing real motion or simply a sequence of static images; both elicit the same level and kind of excitation on the retina.
Film-makers have learnt to exploit this modest limitation of our brain to their advantage. Two exhibits at ACMI particularly illustrated how the limitations of our visual system can be used to represent and transmit motion. The Phenakistiscope, consisting of a wheel in which a series of dragon images were painted on, emulated the apparent movement of the dragon seemingly chasing the ball. Observations showed that this simulation only worked when the wheel was spun with sufficient speed and the dragon was perceived through the small slit. Limiting the aperture allowed us to restrict our focus to the changes that occurred at one particular space over time. Thus, the fast-changing images of the dragon depicting incremental degrees of action could be successfully strung together to portray logical motion. In contrast, not looking through the slit blurred the entire image due to overwhelming excitation on the retina. Similarly, this was how the Tasmanian Tiger Zoetrope was seen under normal lighting; the turntable was spinning too fast to discern the individual movement of the characters. However, when the strobe lights were turned on, it felt as though each of the characters had come to life. This perception is due to a phenomenon known as the Persistence of Vision, which is simply the inability of the retina to follow and signal changing intensities (Gregory,