We covered the auditory system first, comparing with the visual system. The details are in the notes for the last class.

 We then viewed a part of a video on vision which demonstrated that vision occurs in the brain and can be artificially created by stimulation of the skin on a blind person's back outlining what a computerized camera sees in front of the person: initially, he felt the shape on the back itself but eventually the outlines were sensed in his brain. The film also showed some of the work of Hubel and Weisel demonstrating that cells in the visual cortex of a cat serve as feature detectors, only responding to very specific visual stimuli.

• Taste: Until recently, only four flavors were identified as sensed by the gustatory (taste)  mechanisms: salt, sweet, bitter and sour. Salt, sweet and sour are associated with foods our body needs (sugars, NaCl or table salt, and acid foods that often are associated with specific vitamins such as the ascetic acid (Vitamin C) of orange juice. Bitter on the other hand is more of an acquired taste, and is often associated with repellant, inedible or poisonous things. recent research has confirmed something the Japanese have long recognized: there is a fifth flavor, a 'brothy' taste they refer to as 'umami', which is associated with protein foods and 'meaty' flavors.  Taste recptors are located in 'taste buds', nubs of  taste   sensing neurons that are distributed mostly over the surface of the tongue. Theories of the mechanisms in which transduction take place have two forms: the 'lock and key' theory, in which sweet, 'brothy' and bitter molecules fit like keys into precisely shaped receptor sites on the sensory neurons and 'turn them on', cause them to fire. Salty and acidic or sour molecules dissociate into charged ions when in solution in the saliva and these molecules' charged ions flow directly into the taste neurosensors for salt and sour, triggering off the nerve impulses.
• Smell: Unlike the limited range of taste receptors, we have more than 1000 different types of  olfactory (smell) receptors and when you consider that a single 'odor' can be made up of combinations of many these single receptors, you can see that we have a huge range of what we can identify as separate smells. Transduction of smell is triggered by the 'lock and key' mechanism: the fit of the specific molecule to the receptor for that molecule triggers the neuron to fire.

  The olfactory nerve to the brain does not follow the same route as other sensory nerves, in that it does not go first to the cortex of the brain but goes instead first through the amygdala which is part of the limbic system where emotions and memories are initially processed. This explains the power that certain scents have to trigger specific memories and emotions that you associate with that particular odor. Thus, the scent of your first boyfriend or girlfriend's favorite cologne will, years later, instantly conjure up that first time you fell in love.

• The vestibular sense, which originates in part of the inner ear, located next to the auditory mechanisms, is constructed out of structures that are similar to the cochlea, in that they are hollow tubes that are curved, contain fluid and hair-cell-like structures that respond to being bent. The fliud in these three semicircular canals moves when your head moves, which then bends the haircells, sending information to the brain about the position and movement of your head. Gravity hold the fluid in the lower part of these structures, indicating to your brain whether you are standing upright, lying down or standing on your head!  This system helps you maintain your balance.
• The kinesthetic senses give you feedback from muscles and joints that keep your brain in touch with where the body parts are in space and how they are moving.
• The so-called 'skin sensors' involve several different types and forms of receptors that respond to warmth and cold, pressure and light touch to both the skin and the tiny hairs embedded in the skin, and pain. Obviously, some of these receptors are located in other parts of the body, as the skin is not the only place you can sense these particular stimuli, but they are called skin senses as this is  the largest and most varied area of the body where these sensors are located. The skin is our first line of defense against injury as well as an important access route to information about the world in general: information from these senses not only acts as a warning system, it helps us coordinate and confirm information provided by our other senses.

  A baby begins to learn about the connection between the optical information coming from the round object (apple) in front of her when she can reach out and touch it, feel it's smooth surface and the weight of it in her hands. The lips, being the most sensitive of all the skin surfaces, is where she brings this object to explore it in further detail and smell and taste it as well as touch and see it, identifying it after repeated exposure and sensory explorations of all its aspects.

 Review the ways in which the sensory systems limit incoming information: 1)  by gathering, selecting, and  transducing only specific aspects or  features from a limited range of all possible information in the environment, 2)  by adaptation to continuous stimuli (in which the sensory  neurons fire less frequently),  3)  by triggering gates that shut off some incoming messages (pain), and by 4)  use of subconscious perceptual defenses that block unpleasant or upsetting sensations from awareness.. 

 Attention also limits, directs and controls informational intake from the senses, either because of past experiences that lead us to be especially sensitive to certain sensations in specific situations,  making  us more or less aware of them, ( the bark of the dog next door who bit you yesterday is far more noticeable today than it was on the day before it bit you..) or because of internal states that motive us to be more or less aware of specific sensory inputs (When you are on a long drive and you get hungry, you are more likely to notice billboards advertising places to eat.) 

Perception
From the earliest days of our lives, we are constantly organizing our sensations into stable concepts that help us understand and act on/in our environment without having to start from ‘ground zero’ every morning when we wake up. We develop certain perceptions of the world that are stable, in spite of the fact that our senses ‘see’ them differently from different angles, in different lights, etc. The examples that the book gives (the ‘perceptual constancies’) are visual in nature. What are they? What are some examples of these visual constancies? You also have other perceptual constancies. For instance, if I play the first six notes of "Happy Birthday to you..", you can identify the song, not matter what key I play it in, how loud or soft I play it, or how fast or slow I play it. What are some other examples of auditory constancy? Tactile? Think about each of the senses and try to come up with examples of such sensory generalizations you have made.

Our senses bring us huge amounts of data about our internal and external environments. How does our brain then organize all these 'bits' into meaningful patterns such as the 'Happy Birthday" song?

To very young babies, if something cannot be seen, touched, smelled, etc, it does not exist. However, early in life, we learn the concept of ‘object constancy’, that an object does continue to exist even when we can’t see it. Yet first, we have to learn to pick out the object of our attention from its background (Figure/ground perceptions) . Visually, for example, the ability to perceive patterns of line, shape, motion are innate, as are some of the perceptual constancies. (Infants don’t have to learn to pay attention to face-like configurations more that other visual stimuli; this seems to be one of the few innate perceptual abilities of humans.) From sensing and interacting with objects in our environment, we develop the concepts of familiar ‘figures’ (objects or patterns) that can be picked out from their background and that are constant in size, shape and color, despite our constantly changing view of them. We have learned that the friend standing down at the end of dimly lit the hall is the same size and shape, and wearing the same red jacket as when he was sitting hunched up in front of us in a brightly lit classroom a few minutes before. The stimuli received by our sensory mechanisms have changed, but the real size and shape of the person and the color of his jacket have not changed.(For more about the constancies, see size constancy.)

Figure/ground distinctions:
Repeated exposure to groups of stimuli that have a consistent relationship develops a familiarity with those particular patterns  of stimuli. You can think of these patterns as 'figures' against a background of other (unrelated) stimuli. For instance,   the notes of the "Happy Birthday" song, heard in a crowded restaurant, stand out as a pattern or 'figure' against the other sounds, the 'noise' or background. In the same way, a baby becomes familiar, after repeated exposures, with the curves, edges, colors, patterns of light and shadow that make up the pattern (or 'figure') of  a mother's face, and then that face can be picked out of the 'background' of other curves, edges, etc that are not part of that particular pattern of stimuli. (The mother's scent and the sound of her voice are also part of that perception or 'figure' against the background 'noise' of other's voices, the smells of dinner cooking, etc.   THAT face goes with THAT smell and THAT sound....)

Figure/ground, then, is a fundamental way of constructing perceptions from various stimuli.

How do we figure out what stimuli are part of a 'figure' or meaningful pattern and what stimuli are 'background' or 'noise' and NOT part of the 'figure'? The Gestalt psychologists proposed that we are born with some basic abilities for grouping stimuli and organizing them in predictable ways. The goal of this system of organization is to create in our brain the most useful perceptions of our environment. We do this by combining and simplifying the separate elements of sensation into unified and recognizable patterns.

A basic way of organizing the elements we perceive is to group them and our brain operates on some basic 'rules',  or principles, for organizing them into a group of stimuli, (a figure), as well as perceiving separate figures as part of larger groupings. Example: The separate individuals on a basketball team are figures which are part of a larger group or figure, the team.)

GESTALT PRINCIPLES:  There are a number of methods, first identified by the Gestalt psychologists, by which we organize our sensations into perceptions about the world around us. Some of these principles by which we tend to group or classify objects are: 

• proximity (nearness): We group stimuli that are located together in space or time. (Examples: Three people walking together down a crowded sidewalk. A flock of geese at one end of a pond. The notes of the "Happy Birthday" song would not appear to part of  a single song if  the notes were not played close in time; one note an hour would not  add up to that song in your perception.)
• similarity: We tend to group stimuli that share similarities. (Example: We group all the members of one team as they are wearing matching uniforms. Windows can come in all shapes sizes and locations, but they are similar in their function. Chocolate candies may come in many different shapes but the taste is the same.)
• continuity and direction: Our eye tends to want to follow continuously in the same direction and we therefore tend  to perceive stimuli in simplified forms. (In the example in the book at the bottom of page 127, we see two vertical lines with a square in the middle rather than a W sitting on top of an M. Instead of perceiving the separate panels of the ceiling of the classroom, we see the parallel lines their edges make, running across to the far wall. )
• closure: we perceive wholes even when some of the stimuli that complete a figure are not available to our senses. (Example: If I am standing behind a desk so that you can only see my upper body and my feet, you still perceive me as a whole person, not "feet" as separate from "body". And, in the example of an incomplete drawing of an apple, your mind 'closes' the figure into the perception of an apple)
• inclusiveness or common ground:  we tend to group stimuli that make up separate figures into larger simpler figures that include all the separate parts and to perceive items that share the same background as a group. (Example: The basketball player is just one 'piece' of the larger 'figure' of the team.  Another: if you have two fields full of cows next to each other but the fields are owned by two different people, you will perceive two separate herds of cattle, those that belong in Farmer Brown's field and those that belong to Farmer Smith in the next field. The common 'ground' in this case is not only geographic, but ownership. Prejudices come from this phenomena; you tend to group people by where they are from and then to associate them with certain similarities: Farmer Brown's cows are seen as better than Farmer Smith's even though, in fact, Farmer Brown has two very sick cows in his otherwise very fine herd...).
• There are other principles of grouping various stimuli into figure/ground perceptions, such as the shared motion that the spots on the Dalmation dog in the video had: you could not have distinguished the dog from the spotted background if the dog's spots had not been moving together. I will give you only one more:
• Contiguity: next to or near in time or sequence. (Proximity refers to nearness in space.) Contiguity, which we did not discuss in class, should be grouped with these primarily visual principles. It is when different kinds of stimuli occur at the same time or in the same sequence and you learn to associate them together. An example would be the sight and sound of a door slamming:   you (correctly) associate them with the same event or the ‘gestalt’ of that event. During an electrical storm, you see the lightening, then hear the thunder. If you hear an explosion first and then see a flash of light something else is going on....) 

Most of the figure/ground distinctions we make are stable due to the constancies we have learned, but some are not.
Reversible figures: Sometimes a particular set of sensations form a clear figure, but sometimes 'figure' and 'ground' can switch places We looked at a number of visual 'reversible figures': a drawing of an old/young woman, and a man/mouse combination. Sometimes figures don't easily resolve themselves into figure and ground but keep moving back and forth between first one perception and the other, and some people can only see one and not the other.
Impossible figures: Some perceptions are, in fact 'impossible' in real life, but our perceptual habits create illusions. Magic tricks are based on our perceptual habits and expectancies.

A perception is a hypothesis, based upon past experience, until empirical evidence confirms or contradicts it. (Example, one of the people in a group of basketball players who is wearing a team jacket may simply be a friend of a player, someone who got cold and borrowed the jacket, not a team member, but until you have the facts, you may perceive that person as a team member.)

Optical illusions...are based on visual perceptual habits, expectations about the meaning of our sensations based on prior experiences of those sensations.

Visual depth perception is apparently one of the perceptual abilities developed soon after birth. It initially is the result of accommodation (the bending of the lens in the eyes), convergence ( the inward or outward movement of the eyes in focussing on near/far objects) and stereoscopic vision (due to the fact that the two eyes are each getting slightly different views of the world) and the baby’s actual interactions with the nearby environment.

In hearing, we can also sense distance and location in space because, again, we have two ears that receive information at slightly different times; the brain can combine these differences into a ‘3-D’ sense of sound.

In addition to these physiologically-based cues to depth and distance, there are ‘facts’ we learn from our experience about how things look when they are closer or further away. These are called ‘pictorial’ cues (although they occur in reality, not just in pictures) and include 

• interposition, or overlap (of one object ‘in front’ of another), 
• linear perspective (which makes parallel lines look closer together the further away they are from the viewer), 
• relative size (more distant things appear smaller in size), 
• position on the picture plane ( objects above the horizon appear closer when they are higher toward the top of the view or ‘picture’, while things that are below the horizon appear farther away as they are higher toward the top of the view), 
• light and shadow ( which define the 3-dimensionality of objects by the way light falls on them),
•   texture gradient ( the farther away you are from a textured surface, the less you can see the texture and the more the texture appears to flatten out into one simple surface),
• aerial perspective ( when there is moisture, smoke or air pollution in the air, it diffuses the light reflected from objects in the distance more than those nearby, making them appear to be hazy and indistinct).

These learned habits of perception are used by artists to give their drawings and paintings a sense of 3-dimensionality and depth.  For an interest web site on perception, see Vision and Art, a website by  John Krantz, professor at the University of Hanover.

In addition, when you are in motion, motion parallax indicates the distance of an object: things that are farther away appear to move along with you, while things closer to you appear to move away or past you. You can calculate the distance of an object by how fast it appears to be moving. (You are actually what is in motion, not the objects, but that’s not how it looks.  (For an interesting link to this subject, see  The Effects of Shadow. Also, see the websites on MotionParallax and 3d Stereograms )

• These are many of the ways we group or organize incoming stimuli. Most of these examples are visual in nature: we understand the most about vision and up to 70% of the incoming information we have about the world (unlike many other organisms) is visual. When a person has limited sensation from one of his or her senses, the other senses become more important in informing that person about the world. In addition to disability, there are many other factors that influence perception. Obviously, physical illness or injury, exhaustion and stress can affect our senses.

First, our past experiences organize and influence our perceptions. We interpret what we are sensing in terms of similar sensations we have experienced in the past. Our 'constancies' are based on what we have learned in the past, for instance. Just because our friend down the hall looks tiny, we know from past experience that he is not changed in size, but rather that he is farther away, and therefore only appears to be smaller in size.

In addition to teaching us ‘perceptual habits’, where we see what we have come to expect to see based on past experience,  learning affects perception by:

1. alerting us to pay attention
2. improving the ability to tell the difference between very similar stimuli
3. informing us as to what stimuli to notice, what to ignore
4. causing expectations to affect our perceptions. 

A number of visual examples of these Gestalt principles were given in class. However, the same principles of grouping stimuli can be applied to other sensory inputs. The complex scents of a particular flower, a rose, are dependent on the specific proportion of different molecules  given off by that kind of flower that affect the olfactory receptors. These molecules are sensed simultaneously in the olfactory sensors and the brain perceives them as the same pattern of grouped stimuli sensed when previously confronted by the rose. In this situation, while smelling a rose, the smell of the lily and the lilac that are in the same garden are just 'noise', background smells for the 'figure', the scent of the rose, while a person walking by with rose-scented perfume is providing camouflage for the real rose's scent.

WHAT IS REALITY?  Is my reality THE SAME AS YOURS?

What you perceive.... is a perceptual reconstruction by your brain that is uniquely your own: how stimuli from the same source are perceived by different people varies enormously. And, every time you remember a perception, it is updated with new information acquired by your senses since it was first taken in.
When we get to discussing memory, we will consider the implications of this in terms of eye-witness accounts: how reliable are they?