Touch screens eliminate the need for keyboard/mouse combinations which take up valuable space and are prone to failure due to dirt or impact. Because they also present users with fewer response options than the standard keyboard, touch screens have the potential to simplify decision-making at each stage in a sequence. This has the potential advantage of optimizing human performance by minimizing response errors, and maximizing response times.
One major difference between keyboarding and touch screen use involves the role of visual perception. In standard keyboarding, experienced users touch type without looking at the target keys. Touch screen interactions are, however, much more similar to ordinary prehension because they involve making precise reaching movements on the basis of visual input.
Consequently, touch screen performance is likely to be influenced by factors known to affect visually-guided reaching. These include perceptual factors such as the size and distance of the target object, and cognitive factors that affect the speed of decision making.
Understanding how these manipulations influence touch screen behavior is of critical importance when developing software applications in industrial settings.
Reading Assignment One
Keyboards vs. Touch screens. Cognitive scientists working in industrial settings typically begin by analyzing the information processing demands of the particular task that they will be working with. In our case, it will be useful to consider both the similarities and differences between keyboarding and touch screen interfaces.
Within your working groups, discuss the potential consequences of the Speed/Accuracy Tradeoff for human/computer interactions in industrial settings. Under what circumstances might speed of responding be of foremost interest? Under what circumstances might response accuracy be more important than speed?
Before beginning any laboratory exercise, open the TouchWare control panel (normally accessible in the "Control Panels" submenu, off the Apple pull-down menu). In the window that appears:
Therefore, it is of interest to determine how these variables affect touch screen performance. Is there an optimal object size and distance of the actor from the screen that facilitates the speed of touch screen responses without compromising accuracy? In an attempt to address this question, you will explore the effects of independently manipulating the dimensions and distance of a visually presented target object on touch screen response time.
The two scripts represent identical versions of the experiment, with one exception: The script entitled "Far.script" begins with subjects positioning their response hand on the far starting position (40 cm from the screen on the desktop). The script entitled "Near.script" begins with subjects positioning their hands in the near starting position (20 cm from the screen on the desktop).
For purposes of counterbalancing, half of your subjects should be run with the "Far.script," file and the remaining half should be run with the "Near.script" file. In both cases, subjects will receive instructions on the screen regarding the hand position for each part of the exercise.
Before running the experiment you will need to mark the two starting positions (20 and 40 cm from the screen) on the desktop in the front and center of the monitor.
To begin Laboratory Exercise One, double-click on one of the script files (Far.script or Near.script) in the Exercise One folder. The SuperLab program will start, and the SuperLab Experiment Editor window will open.
DO NOT MAKE ANY CHANGES within the SuperLab Experiment Editor display and DO NOT press on the buttons at the bottom of the window.
When the SuperLab Experiment Editor window opens, go to the Experiment pull-down menu, and select Run. A different window will now open. This window allows you to enter the subject's name. Type in a unique name or designation for the subject and press the Run button in the window.
Another window will appear. This window allows you to specify where the results of the laboratory exercise will be saved, and what will be the name of the file in which the results will be saved.
First, at the top of the window, scroll down until the name of your Zip disk appears. Your data files must all be stored on your Zip disk(s). Data files and other personal files on the computer's hard drive will be erased.
Second, type in a unique name for the data file that will be created, replacing the default file name that automatically appears. Each data file must have a different, unique name. If two files have identical names, the more recent file will replace and destroy the older file. To avoid this problem, you could use a file name such as: Ex1Near1stJRS1 to designate a Laboratory Exercise One (Ex1) data file in which the Near condition came first (Near1st) for subject Jennifer R. Smith's (JRS) first set of trials (1). If the same Laboratory Exercise and Near first condition were repeated for the same subject, the next file name might be named Ex1Near1stJRS2.
After the location for saving the data file and the data file's name have been specified, the experiment automatically begins. Instructions will appear on the screen. Starting at this time, and continuing until all the trials of this laboratory exercise have occurred, the computer keyboard will become inoperative. Only input from touching the screen or from the mouse will have any effect.
Note: It is important to turn off all unnecessary applications (including a screen saver if one is present) before running an experiment.
The subject's task will be to contact the center of the target circle as quickly as possible with the index finger of their dominant hand. Response times will be measured from the onset of the target object, until the subject contacts the screen of the display monitor. Be certain to emphasize that the subject should continue to touch the screen until the stimulus object(s) disappear.
Within each block, subjects will respond to circles of 1, 3, or 5 cm in diameter. Each size circle will appear in all four different locations within each block. Both the size of the circle and its location will vary randomly within each block of trials.
Each subject will perform seven blocks of trials beginning with their hand in the near starting position (20 cm from the screen), and another seven blocks with their hand in the far starting position (40 cm from the screen).
When all trials have been presented, the words "THE END!" will appear on the screen. At this time, touching the screen anywhere will produce a return to the normal SuperLab environment, and the keyboard will be useable.
In summary, this experiment consists of three independent variables: target size, target location, and distance of the response hand from the screen.
Refer to the Appendix for information pertaining to data analysis.
Questions
In the previous exercise, it was shown that the time to respond to a stimulus increased as a function of both the size and distance of the target. A typical touch screen interaction, however, usually requires that the user choose from among a number of response options. In other words, touch responses typically involve choice, not just simple response times.
The number of response options confronting the actor is known to affect the time course of choice response times. More precisely, choice response time increases linearly with the logarithm (taken to the base 2 so that it can be interpreted as bits of information) of the number of response alternatives. This relationship is known as the Hick-Hyman Law, and has been shown to accurately describe human performance in numerous situations.
Designers of touch screen applications are confronted with the issue of how many response options to include in a single display. Including more response options in a single display has the advantage of requiring fewer responses from the actor, but has the potential disadvantage of greatly increasing the time required for any single response. Conversely, having only a small number (e.g., two) response options in each display facilitates each decision, but demands many more actual responses by the actor.
In the present exercise, you will examine the effects of increasing the number of response options on the time course of touch screen performance. Your goal will be to determine whether there is there a certain number of response options that represents an ideal compromise between the number and speed of responses within a single display.
Open the folder entitled "Touch screen Lab." Within that folder, open the folder entitled "Exercise two." In this folder you will find the SuperLab script for running the experiment in a file named "Lab2.script", and a folder entitled "stimuli" which contains all of the stimulus files. To begin Laboratory Exercise Two, double-click on the script file entitled "Lab2.script". The SuperLab program will start, and the SuperLab Experiment Editor window will open.
DO NOT MAKE ANY CHANGES within the SuperLab Experiment Editor display and DO NOT press on the buttons at the bottom of the window.
When the SuperLab Experiment Editor window opens, go to the Experiment pull-down menu, and select Run.
A different window will now open. This window allows you to enter the subject's name. Type in a unique name or designation for the subject and press the Run button in the window.
Another window will appear. This window allows you to specify where the results of the laboratory exercise will be saved, and what will be the name of the file in which the results will be saved.
First, at the top of the window, scroll down until the name of your Zip disk appears. Your data files must all be stored on your Zip disk(s). Data files and other personal files on the computer's hard drive will be erased.
Second, type in a unique name for the data file that will be created, replacing the default file name that automatically appears. Each data file must have a different, unique name. If two files have identical names, the more recent file will replace and destroy the older file. To avoid this problem, you could use a file name such as: Ex2JRS1 to designate a Laboratory Exercise Two (Ex2) data file in which the subject Jennifer R. Smith's (JRS) first set of trials (1). If the same Laboratory Exercise Two were repeated for the same subject, the next file name might be named Ex2JRS2.
After the location for saving the data file and the data file's name have been specified, the experiment automatically begins. Instructions will appear on the screen. Starting at this time, and continuing until all the trials of this laboratory exercise have occurred, the computer keyboard will be inoperative. Only input from touching the screen or from the mouse will have any effect.
Note: It is important to turn off all unnecessary applications (including a screen saver if one is present) before running an experiment.
The subject's task will be to select the comparison object that is identical in shape to the previous standard object as quickly and accurately as possible with the index finger of their dominant hand. Response times will be measured from the onset of the target object, until the subject contacts the monitor. Be certain to emphasize that the subject should continue to touch the screen until the stimulus object(s) disappear.
Following each trial, there will be an intertrial interval of 5 sec., during which the subject will return their hand to the designated starting position.
After completing the second block of trials, a message will appear giving the subject the option of taking a brief rest.
Each subject will complete four blocks of 30 trials. These 30 trials were created by crossing three possible target locations (left, center, right) by all possible one, two, and three item combinations. In the results files, you will see a digit representing the position of the correct target object (1=left, 2=center, 3=right), and another digit representing the number of items in the comparison display (1,2, or 3).
When all trials have been presented, the words "THE END!" will appear on the screen. At this time, touching the screen anywhere will produce a return to the normal SuperLab environment, and the keyboard will be useable.
Refer to the Appendix for information pertaining to data analysis.
Questions
An interesting question concerns how the number of shared properties between response objects influences touch screen response times. That is, are subjects faster when they are required to make successive responses to stimuli that have the same shape, same color, or both properties in common? This is a potentially important issue when developing touch screen operations.
In many programs, there is a standard path of responses that must be made repeatedly by the operator. To facilitate speed of performance in these decisions, it would be helpful to know how shared perceptual properties affect choice response times. This information could be used to help operators navigate rapidly through the standard decision path.
Conversely, in some situations, automatic responding is highly undesirable. Instead, it is necessary to design applications that force operators to be more deliberate in making their choice responses, with the goal of avoiding unnecessary mistakes. By understanding how the perceptual characteristics of stimuli affect the speed of successive choice response times, it should be possible to develop software applications that meet either of these goals.
One way to approach this issue involves exploring the effects of manipulating the shape or color of target objects on the time required to successfully match items across successive displays.
Open the folder entitled "Touch screen Lab." Within that folder, open the folder entitled "Exercise three." In this folder you will find two files "color.script," and "shape.script", containing the SuperLab script for running the experiment, and a folder entitled "stimuli" which contains all of the stimulus files. To begin Laboratory Exercise Three, double-click on either the script entitled "color.script," or the script entitled "shape.script" in the Laboratory Exercise Three folder. Be sure to follow the counterbalancing procedure described in the Methods section below.
The SuperLab program will start, and the SuperLab Experiment Editor window will open.
DO NOT MAKE ANY CHANGES within the SuperLab Experiment Editor display and DO NOT press on the buttons at the bottom of the window.
When the SuperLab Experiment Editor window opens, go to the Experiment pull-down menu, and select Run.
A different window will now open. This window allows you to enter the subject's name. Type in a unique name or designation for the subject and press the Run button in the window.
Another window will appear. This window allows you to specify where the results of the laboratory exercise will be saved, and what will be the name of the file in which the results will be saved. First, at the top of the window, scroll down until the name of your Zip disk appears. Your data files must all be stored on your Zip disk(s). Data files and other personal files on the computer's hard drive will be erased.
Second, type in a unique name for the data file that will be created, replacing the default file name that automatically appears. Each data file must have a different, unique name. If two files have identical names, the more recent file will replace and destroy the older file. To avoid this problem, you could use a file name such as: Ex3color1stJRS1 to designate a Laboratory Exercise Three (Ex3) data file in which the color condition came first (color 1st) for subject Jennifer R. Smith's (JRS) first set of trials (1). If the same Laboratory Exercise Three and color first condition were repeated for the same subject, the next data file name might be Ex3color1stJRS2
After the location for saving the data file and the data file's name have been specified, the experiment automatically begins. Instructions will appear on the screen. Starting at this time, and continuing until all the trials of this laboratory exercise have occurred, the computer keyboard will be inoperative. Only input from touching the screen or from the mouse will have any effect.
Note: It is important to turn off all unnecessary applications (including a screen saver if one is present) before running an experiment.
For purposes of counterbalancing, two versions of the experiment were created: The script entitled "color.script" begins with a color block, while the script entitled "shape.script" begins with a shape block. Half of the subjects should be run with one version, and half with the other.
On each trial, three comparison objects will appear in the left, center and right locations on the screen. Subjects will be required to select the object that is consistent with the cue word from among the three comparison items. These comparison items always differ from one another in both color and shape. Response time will be recorded from the onset of the comparison items until the subject contacts the screen with the index finger of their dominant hand.
If the subject makes no response within 3000 ms, the trial is considered erroneous, and the program automatically advances to the next trial. There is a 3000 ms intertrial interval during which time subjects should return their response hand to the starting position and prepare for the next trial. Be certain to emphasize that the subject should continue to touch the screen until the stimulus object(s) disappear.
The study has been designed such that all possible shape and color combinations are presented within each block of trials. Likewise, on a given trial each color and shape has an equal probability of occurring in any one of the three possible locations.
When all trials have been presented, the words "THE END!" will appear on the screen. At this time, touching the screen anywhere will produce a return to the normal SuperLab environment, and the keyboard will be useable
Refer to the Appendix for information pertaining to data analysis.
Questions
Two articles have been selected to stimulate your thinking. These particular articles were chosen because they summarize interdisciplinary research on the problem of coordinating visual perception and hand movements, and present provocative theories of how this task is accomplished by the brain. Even if you already have an idea of what you would like to do, these papers will be helpful in refining your hypothesis and developing an experiment.
If you are stuck, a few interesting questions to explore might include:
Laboratory Exercises One through Three should be included in your report either as part of a series of formal experiments, including statements of methods, full results, and brief discussions, or as 'preliminary experiments', alluded to but not presented in any detail.
In either case, the results of Laboratory Exercise Four should be presented in detail, all results discussed, and appropriate conclusions drawn. If you choose to include exercises one through three as part of the series of regular experiments, there should be a final general discussion section for all four experiments.
Fitts, P.M. (1954). The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 47, 381-391.
Goodale, M. A., & Milner, A.D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15, 20-25.
Hyman, R. (1953). Stimulus information as a determinant of reaction time. Journal of Experimental Psychology, 45, 188-196.
Jeannerod, M. (1997). Grasping objects: The hand as a pattern recognition device. In M-C, Hepp-Reymond & G. Marini (eds.). Perspectives of motor behavior and its neural basis, pp. 19-32. Basel, Karger. Rosenbaum, D.A. (1991). Human Motor Control. New York: Academic. Chapter 8, pp. 253 - 264.
Experiment One. The starting position of the subject's response hand was varied in this experiment, as well as the size and position of the stimulus circle. Subjects alternated blocks using either the "near" or "far" starting position. For each block of trials you will need to determine whether it was a "near" or "far" block.
This can be done by looking at the line above the first stimulus item within each block; it will be labeled either "near" or far." (These lines, as well as others corresponding to instructions, rest breaks, etc. should be removed from the output before you analyze the data). You will then need to create another column in Excel that codes the starting position for each block; e.g., 1 = near, 2 = far.
In the results files you will see the three part names of each stimulus event, e.g., "1cm.low.lft." The first part of the name refers to the diameter of the circle. The second part of the name refers to the vertical position of the stimulus (either low or high). The final part of the name refers to the horizontal position of the stimulus (either lft = left, ct = center, or rt = right). So, a stimulus labeled "1cm.low.lft" means that a 1 centimeter circle appeared in the lower left position on the screen.
Experiment Two. In the second experiment two variables were manipulated: the number of items in the display (1,2, or 3), and the horizontal position of the target item on the screen (left, center, or right).
You will find two codes representing this information for each trial. The code entitled "item" refers to the number of stimulus objects in the display (1,2, or 3). The code labeled "position" refers to the horizontal position of the target (or correct) stimulus object. the numeral 1 = left, 2 = center, and 3 = right.
Experiment Three. Both the color and shape of the items were varied in this experiment. To analyze the data you will need to know how the target object was defined for each block; i.e., is it a color block (e.g., "blue"), or is it a shape block (e.g., "square")? Recall that subjects alternated between blocks where the stimulus was defined by its color, and blocks where the stimulus was defined by its shape.
You can find this information at the beginning of the data column for each block of trials. The first stimulus event within each block will designate the identity of the target for trials contained within that block (e.g., "blue," or "square"). You will then need to create your own column in Excel that codes this blocked variable.
Trials within a block all consist of three items that have different locations, colors and shapes. The name of a stimulus contains information about all three of these variables. For instance, a trial which contains the event "bcir.rdiam.gsq" consists of a blue circle on the left, a red diamond in the center, and a green square on the right. When analyzing your data you can create separate variables using Excel that represent these three different pieces of information.