Idiot Brain by Dean Burnett Page B

system can chip in and say if it’s a familiar face or not, too. Another common illusion makes two things that are exactly the same color look different when placed on different backgrounds. This can be traced to the secondary visual cortex getting confused.
    Other visual illusions are more subtle. The classic “is it two faces looking at each other or actually a candlestick?” image is possibly the most familiar. This image presents two possible interpretations, both images are “correct” but are mutually exclusive. The brain really doesn’t handle ambiguity well, so it effectively imposes order on what it’s receiving by picking one possible interpretation. But it can change its mind, too, as there are two solutions.
    All this barely scratches the surface. It’s not really possible to convey the true complexity and sophistication of the visual-processing system in a few pages, but I felt it worth the attempt because vision is so complex a neurological process that underpins so much of our lives, and most people think nothing of it until it starts going awry. Consider this section just the tip of the iceberg of the brain’s visual system; there’s a vast amount more in the depths below it. And you can perceive such depths only because the visual system is as complex as it is.
    Why your ears are burning
    (Strengths and weaknesses of human attention, and why you can’t help eavesdropping)
    Our senses provide copious information but the brain, despite its best efforts, cannot deal with all of it. And why should it? How much is actually relevant? The brain is an incredibly demanding organ in terms of resources, and using it to focus intently on a patch of drying paint would just squander them. The brain has to pick and choose what gets noticed. As such, the brain is able to direct perception and conscious processing to things of potential interest. This is attention, and how we use it plays a big role in what we observe of the world around us. Or, often more importantly, what we fail to observe.
    For the study of attention, there are two important questions. One is, what’s the brain’s capacity for attention? How much can it realistically take in before it gets overwhelmed?The other is, what is it that determines where the attention is directed? If the brain is constantly being bombarded with sensory information, what is it about certain stimuli or input that prioritizes it over other things?
    Let’s start with capacity. Most people have noticed attention has a limited capacity. You’ve probably experienced a group of people all trying to talk to you at once, “clamoring for attention.” This is frustrating, usually resulting in loss of patience and shouts of, “One at a time !”
    Early experiments, such as those by Colin Cherry in 1953, 10 suggested attention capacity was alarmingly limited, demonstrated by a technique called “dichotic listening.” This is where subjects wear headphones and receive a different audio stream (typically, a sequence of words) in each ear. They were told they had to repeat the words received in one ear, but then were asked what they could recall from the other ear. Most could identify whether the voice was male or female, but that’s it, not even what language was spoken. So attention has such a limited capacity, it can’t be stretched beyond a single audio stream.
    These and similar findings resulted in “bottleneck” models of attention, which argued that all the sensory information that is presented to the brain is filtered through the narrow space offered by attention. Think of a telescope: it provides a very detailed image of a small part of the landscape or sky. But, beyond that, there’s nothing.
    Later experiments changed things. Von Wright and his colleagues in 1975 conditioned subjects to expect a shock when they heard certain words. Then they did the dichotic-listening task. The