Psychology - Perception & Sensation

In this video, we're learning about perception and sensation. So we'll cover the difference between sensation and perception, bottom-up and top-down processing, and finally, depth perception. Let's start by understanding the difference between sensation and perception. We use the term sensation to describe the detection of stimuli through our sensory receptors. Put simply, it's the process of receiving raw information from the environment. So this includes things like light hitting your eyes, Your sensory receptors pick up these physical signals and convert them into nervous signals that get sent to your brain. Then we have perception, which is what happens after sensation. So it's how your brain interprets and organizes sensory information into something meaningful. Basically, while sensation is about receiving information, perception is about making sense of it. For example, let's say you're listening to music. The sensation part is your ears detecting sound waves and converting them into nervous signals that get sent to your brain. The perception part is your brain interpreting those signals as music, recognizing the melody, and perhaps triggering an emotional response. There are two different ways our brain handles the information we receive from our senses. Bottom-up processing and top-down processing. Bottom-up processing is data-driven, which means we build our perception from the ground up using raw sensory input. The process starts with the stimulus itself, and our brain pieces information together without relying on prior knowledge or expectations. Let's say you hear a strange sound in the middle of the night. In cases of bottom-up processing, you'd start by processing the raw qualities of that sound, like whether it's high or low-pitched, loud or quiet, and where it seems to be coming from, building up your understanding from these basic sensory features. For top-down processing, this works in the other direction. It's expectation-driven, which means we use our prior knowledge, experiences, and expectations to interpret what we're sensing. As an example, if you know your cat likes to knock things off shelves, you might immediately assume a late-night crash is your cat, without needing to analyze all the individual qualities first. Another important concept that relates to top-down processing is perceptual set, which refers to how our expectations shape what we actually perceive. Your perceptual set is influenced by factors like your past experiences, your current emotional state, and the context you're in. So going back to our example, if you'd recently watched a scary film, you might be more likely to perceive that sound in the night as something threatening, whereas if you're feeling relaxed, you're more likely to assume it's something harmless, like the cat. So far we've looked at two different ways our brains process sensory information, and part of this processing involves actively organizing what we perceive into meaningful patterns. So if we think about how our brains organize information, one of the ways is via something called Gestalt principles. Gestalt principles describe how we naturally group elements together to perceive whole patterns, rather than disconnected parts. And there are four main principles you need to know about. First, proximity is when we group objects that are physically close together. So if you see a cluster of dots near each other, you perceive them as belonging to the same group. Similarity is when we group objects that look alike. So if some of those dots are blue, and some are yellow, you'd group the blue dots together, and the yellow dots together. Third, closure is our tendency to fill in gaps to perceive complete shapes. So if the dots are arranged in a circular pattern with spaces between them, you'd still perceive them as forming a circle. Then fourth, continuation is when we perceive smooth, continuous lines, rather than abrupt changes in direction. So if the dots are arranged in a circle, the part of that circle is hidden behind another shape, you'd perceive the dots as continuing in that same curved path behind it, rather than suddenly veering off in a different direction. Finally, let's look at depth perception, which is our ability to see the world in three dimensions and judge how far away objects are. To do this, our brain relies on what we call depth cues, which are basically visual signals that help us perceive distance. There are two main types of depth cues, monocular cues and binocular cues. Monocular depth cues are cues that only require one eye to perceive. An example is linear perspective, which is when parallel lines appear to converge as they get farther away, like railway tracks seeming to meet at the horizon. Other monocular cues include relative size, where closer objects appear larger, and texture gradient, where surfaces appear smoother and less detailed as they recede into the distance. On the other hand, binocular cues require both eyes working together. The main binocular cue is retinal disparity, which happens because our two eyes are positioned a few centimeters apart, meaning each eye sees things from a slightly different angle. This is why when you hold up your finger in front of your face and close one eye, then switch to close the other eye instead, your finger appears to jump from side to side against the background, because each eye is viewing it from a different position. Your brain combines these two slightly different views to calculate how far away objects are, giving you a sense of depth. Gibson and Walk in 1960 investigated whether depth perception is innate or learned. They designed what became known as the visual cliff apparatus, which was a table with a glass surface. One half had a checked pattern directly beneath the glass, which was the shallow side, while the other half had the pattern several feet below, creating the appearance of a cliff or sudden drop. In their procedure, infants aged between 6 and 14 months were placed on the shallow side, and their mothers encouraged them to crawl across to the deep side. The findings showed that most infants refused to crawl over the visual cliff, even when their mothers called to them from the other side. These findings support the idea that depth perception develops early in life, suggesting it may be innate, or at least develops very quickly. A limitation of this study though, is that because the infants tested were at least 6 months old and already crawling, it's difficult to determine whether depth perception is truly innate, or whether it developed through experience during those first few months of life. So, sign up for free by clicking here, or browse our playlist here on YouTube.