Information Processing, Human Error and the Learning Process — Page 147, Lesson 236

I want to walk you through how our brain takes in information from the world around us, starting with the very first step: the stimuli that come in through our senses. We have five senses — sight, hearing, taste, smell, and touch — and each one provides inputs, which we call stimuli, to our brain. Now, here's a key point: most stimuli are stored for a brief time even after the input has finished. That ability to hold onto them for a short while is essential, because when stimuli first arrive, we may not have the processing capacity to deal with them immediately. The brain needs a moment to catch up. But not every stimulus gets through. A stimulus must be of a certain strength for the sensory receptors to pick it up. For example, a sound has to be loud enough to be heard, or a light level bright enough to be seen. That minimum strength is called the sensory threshold. Below that threshold, your senses simply don't register it. Now, once stimuli do get in, they enter our memory system. There are three types of memory: sensory memories, sometimes called ultra short-term memories; short-term memory, also known as working memory; and long-term memory. We're going to focus on the first type right now. Let's talk about the receptors and sensory memories or stores. The key features are: first, there is a separate memory store for each sensory system — sight has its own, hearing has its own, and so on. Second, the input in these stores decays rapidly. It doesn't hang around for long. In aviation, the sensory stores for touch, taste, and smell are of little significance. But the stores for sight and sound are very important, and we need knowledge of them. So let's discuss both. First, the sensory memory for sound is called the echoic memory. This is the longest lasting sensory store, and it can last for between 2 and 8 seconds. The echoic memory retains sounds, and here's a classic example: imagine you hear a clock chiming the hour. You might not consciously count the strokes as they happen, but after the third or fourth stroke, you realise you want to know the time. You can then mentally 'replay' the echoic memory to count the strokes consciously. So the echoic memory can be interrogated or replayed. It needs to last long enough for the input to be scanned for relevance. If an input is of interest, it gets called into short-term memory for further processing. Second, the sensory memory for sight is called the iconic memory. This is the visual sensory store, and it only lasts for between 0.5 and 1 second. That's very brief. And here's a striking statistic: 80% of information processed by man enters the visual channel. So in aviation, your eyes are your primary source of information, but that iconic memory is extremely short-lived. Finally, there's a special characteristic of all sensory receptors called sensory adaptation, sometimes referred to as habituation. Here's what happens: when a continuous stimulus is first applied, the receptors respond at a very high impulse rate at first. Then they progressively respond less rapidly, until finally many of them no longer respond at all. That's why, once you get dressed, you don't continue to feel your clothes against your skin — your touch receptors have adapted. The classic example in aviation is moving into a house close to a railway line or an airport. At first, the noise of passing trains or departing aircraft can cause extreme stress. But after living there for a month or so, the noise may be hardly sensed, if at all. Your auditory receptors have adapted. That's sensory adaptation, or habituation, in action.