HCI-lect-02.pdf

HCI Lecture 02 1 INTRODUCTION We start with the human, the central character in any discussion of interactive systems. The human, the user, is the one whom computer systems are designed to assist. The requirements of the user should therefore be our first priority. 2 INTRODUCTION In order to design...

HCI Lecture 02 1 INTRODUCTION We start with the human, the central character in any discussion of interactive systems. The human, the user, is the one whom computer systems are designed to assist. The requirements of the user should therefore be our first priority. 2 INTRODUCTION In order to design something for someone, we need to understand their capabilities and limitations. We need to know if there are things that they will find difficult or, even, impossible. We will look at aspects of cognitive )‫(ادراكى‬psychology which have a bearing )‫(تحمل‬ on the use of computer systems: 3 INTRODUCTION how humans perceive the world around them, how they store and process information and solve problems, and how they physically manipulate objects. In 1983, Card, Moran and Newell described the Model, Human Processor Model, which is a simplified view of the human processing involved in interacting with computer systems. The model comprises three subsystems: 4 INTRODUCTION – the perceptual system ) ‫(نظاا االدراكداالدسى اا‬, handling sensory stimulus )‫ (التحفيز‬from the outside world, – the motor system ) ‫(دسنظااا االدسىك ااا‬, which controls actions, – the cognitive system) ‫(النظ ا الالمفر ا‬, which provides the processing needed to connect the perceptual system and the motor system. Each of these subsystems has its own processor and memory, although obviously the complexity of these varies depending on the complexity of the tasks the subsystem has to perform. 5 INTRODUCTION The model also includes a number of principles of operation which dictate the behavior of the systems under certain conditions. We will use the analogy of the user as an information processing system, but in our model make the analogy closer to that of a conventional )‫(تقليدى‬computer system. Information comes in, is stored and processed, and information is passed out. We will therefore discuss three components of this system: input–output, memory and processing. 6 INTRODUCTION In the human, we are dealing with an intelligent information-processing system, and processing therefore includes problem solving, learning, and, consequently, making mistakes. In this lecture, we will first look at the human’s input–output channels, the senses and responders or effectors. 7 INTRODUCTION In other lectures, we will consider human memory and how it works. We will then think about how humans perform complex problem solving, how they learn and acquire skills, and why they make mistakes. Finally, we will discuss how these things can help us in the design of computer systems. 8 INPUT–OUTPUT CHANNELS A person’s interaction with the outside world occurs through information being received and sent: input and output. In an interaction with a computer the user receives information that is output by the computer, and responds by providing input to the computer. Input in the human occurs mainly through the senses and output through the motor control of the effectors. 9 INPUT–OUTPUT CHANNELS There are five major senses: sight )‫ (البصر‬, hearing, touch, taste and smell. Of these, the first three are the most important to HCI. Taste and smell do not currently play a significant role in HCI. However, vision, hearing and touch are central. Similarly there are a number of effectors, including the limbs )‫(اطراف‬, fingers, eyes, head and vocal )‫ (الصوت‬system. 10 INPUT–OUTPUT CHANNELS In the interaction with the computer, the fingers play the primary role, through typing or mouse control, with some use of voice and eye, head and body position. Imagine using a personal computer (PC) with a mouse and a keyboard. The application you are using has a graphical interface, with menus, icons and windows. In your interaction with this system you receive information primarily by sight, from what appears on the screen. 11 INPUT–OUTPUT CHANNELS However, you may also receive information by ear: for example, the computer may ‘beep’ at you if you make a mistake or to draw attention to something, or there may be a voice commentary in a multimedia presentation. Touch plays a part in that you will feel the keys moving (also hearing the ‘click’) or the orientation of the mouse, which provides vital feedback about what you have done. 12 INPUT–OUTPUT CHANNELS You yourself send information to the computer using your hands, either by hitting keys or moving the mouse. Sight and hearing do not play a direct role in sending information in this example, although they may be used to receive information from a third source (for example, a book, or the words of another person) which is then transmitted to the computer. 13 INPUT–OUTPUT CHANNELS In this section we will look at the main elements of such an interaction, first considering the role and limitations of the three primary senses and going on to consider motor control. 14 Vision Human vision is a highly complex activity with a range of physical and perceptual limitations, yet it is the primary source of information for the average person. We can roughly divide visual perception into two stages: – The physical reception of the stimulus from the outside world. – The processing and interpretation of that stimulus. 15 Vision On the one hand the physical properties of the eye and the visual system mean that there are certain things that cannot be seen by the human. On the other the interpretative capabilities of visual processing allow images to be constructed from incomplete information. 16 The human eye We will begin by looking at the eye as a physical receptor, and then go on to consider the processing involved in basic vision. – Vision begins with light. The eye is a mechanism for receiving light and transforming it into electrical energy. – Light is reflected from objects in the world and their image is focused upside down on the back of the eye. – The receptors in the eye transform it into electrical signals which are passed to the brain. 17 Visual perception Understanding the basic construction of the eye goes some way to explaining the physical mechanisms of vision but visual perception is more than this. CLICK HERE 18 Visual perception we will look a little more closely at how we perceive size and depth, brightness and color, each of which is crucial to the design of effective visual interfaces. 19 Perceiving size and depth Imagine you are standing on a hilltop. Beside you on the summit you can see rocks, sheep and a small tree. On the hillside is a farmhouse with outbuildings and farm vehicles. Someone is on the track, walking toward the summit. Below in the valley is a small market town. Our visual system is easily able to interpret the images which it receives to take account of these things. We can identify similar objects regardless of the fact that they appear to us to be of vastly different sizes. In fact, we can use this information to judge distances. 20 Perceiving size and depth So how does the eye perceive size, depth and relative distances? To understand this we must consider how the image appears on the retina )‫(شبكةلالفين‬. As we noted in the previous section, reflected light from the object forms an upside-down image on the retina. The size of that image is specified as a visual angle. Figure 1.2 illustrates how the visual angle is calculated. 21 22 Perceiving size and depth If we were to draw a line from the top of the object to a central point on the front of the eye and a second line from the bottom of the object to the same point, the visual angle of the object is the angle between these two lines. Visual angle is affected by both the size of the object and its distance from the eye. Therefore if two objects are at the same distance, the larger one will have the larger visual angle. Similarly, if two objects of the same size are placed at different distances from the eye. 23 Perceiving brightness A second aspect of visual perception is the perception of brightness. Brightness is in fact a subjective reaction to levels of light. It is affected by luminance )‫ (االن رة‬which is the amount of light emitted )‫(منبفث‬by an object. 24 Perceiving brightness Luminance is a physical characteristic and can be measured using a photometer. Contrast )‫ (تن قض‬is related to luminance: it is a function of the luminance of an object and the luminance of its background. Visual acuity )‫ (ىاةالدسبصك‬increases with increased luminance. This may be an argument for using high display luminance. However, as luminance increases, flicker )‫(رمش‬also increases. The eye will perceive a light switched on and off rapidly as constantly on. 25 Perceiving color A third factor that we need to consider is perception of color. Color is usually regarded as being made up of three components: hue)‫(درجةلاللون‬, intensity )‫ (الشدة‬and saturation )‫(التشبع‬. Hue is determined by the spectral)‫(طيفى‬ wavelength of the light. Blues have short wavelengths, greens medium and reds long. 26 Perceiving color Approximately 150 different hues can be discriminated by the average person. Intensity is the brightness of the color. Saturation is the amount of whiteness in the color. By varying these two, we can perceive in the region of 7 million different colors. 27 The capabilities and limitations of visual processing In considering the way in which we perceive images we have already encountered some of the capabilities and limitations of the human visual processing system. Visual processing involves the transformation and interpretation of a complete image, from the light that is thrown onto the retina. 28 The capabilities and limitations of visual processing This ability to interpret and exploit our expectations can be used to resolve ambiguity )‫(التب س‬. For example, consider the image shown in Figure 1.3. What do you perceive? Now consider Figure 1.4 and Figure 1.5. 29 The capabilities and limitations of visual processing 30 The capabilities and limitations of visual processing 31 32 The capabilities and limitations of visual processing 33 The capabilities and limitations of visual processing 34 The capabilities and limitations of visual processing However, it can also create optical illusions. For example, consider Figure 1.6. Which line is longer? Most people when presented with this will say that the top line is longer than the bottom. In fact, the two lines are the same length. This may be due to a false application of the law of size constancy: the top line appears like a concave edge, the bottom like a convex edge. A similar illusion is the Ponzo illusion (Figure 1.7). Here the top line appears longer, owing to the distance effect, although both lines are the same length. These illusions )‫(أوه ال‬demonstrate that our perception of size is not completely reliable. 35 The capabilities and limitations of visual processing 36 Thank you 37