**5.1 What is heaviness?**

Various physical attributes are involved in the perception of heaviness of objects, leading to an understanding that psychological heaviness is not equal to physical weight. Heaviness perception is not simply a function for sensing object weight. Rather it functions as a form of recognition of the object. That is, all information obtained synchronously when humans grasp and lift an object may be gathered across modalities, integrated with or subtracted from each other, interpreted by object knowledge, and then formed as perceived heaviness.

Among physical properties influencing heaviness, rotational inertia can be considered vital for future investigation, given evidence rotational inertia firmly affects heaviness (Turvey & Carello, 1995; Amazeen, 1999; Streit et al., 2007; Cf. Zhu & Bingham, 2011). However, such evidence has not explained neurologically how it is obtained from lifting, holding and manipulating an object and how it contributes to forming its heaviness. Gaining an understanding of how humans process the information about the rotational inertia of objects

Computer Graphic and PHANToM Haptic Displays:

perception, e.g., object recognition.

experience on earth.

**6. Acknowledgments** 

physical objects.

Powerful Tools to Understand How Humans Perceive Heaviness 41

3. These devices can accurately isolate or focus on only one single factor from all factors possible. Such a result is often impossible or exceptionally hard to accomplish with only

4. These devices can present stimuli with a considerably wider range of intensity or even in smaller increments than physical stimuli. Thus, they can act on the sensorimotor and perceptual systems of individuals for whom sensitivities or discriminative abilities are quite different. In the physical world, individual variability in sensitivity sometimes prevents the uncovering of mechanisms underlying the perceptual system. That is, it is often the case that the intensities determined by the experimenters are sufficient for some humans to detect and discriminate, but not others. However, it is almost impossible to cover all the range of intensities of stimuli using hundreds of physical objects. In this sense, these devices are powerful tools for obtaining detailed assessments of the discriminative ability of human perception and for users of

5. These devices can quickly, in a timely, constant and invariant manner, vary or exchange a part or the whole of multimodal stimuli, for presentation to humans. This is also advantageous, compared to the physical environment, to the tasks in which subjects are required to compare two or more bits of sensory information among all the stimuli presented. This may elucidate the mechanisms of multimodal integration and unitary

6. These computer devices could possibly generate and present a stimulus possessing a weight-size relationship or an incredible density that humans are physically unable to

7. These devices enable accurate, precise and high resolution temporal and spatial

In the history of the development of haptic interfaces, little or no concern seems to have been paid to the human unit of heaviness. Instead, haptic devices - including robot hands and arms - have been developed based on the machine-centered unit of weight and reflected forces. This seems to hold true also for psychologists who have termed all psychological phenomena as illusions and have avoided interpreting them based on biological or physiological views. Of course, such weight-based devices have assisted humans to lift or manipulate a variety of objects in a smooth and safe manner. This success seems to depend, in large part, on efforts of users via their adaptation and/or learning systems, rather than via the engineered haptic systems. In the future, however, users of haptic devices will certainly include those lacking the abilities of adaptation and/or learning such as the elderly, the physically challenged, and medical patients who cannot easily adjust to such computer-centered systems. Thus, such systems developed in the future should be humancentered. Ideally such haptic devices should be suited for adaptation to the human haptic systems, to perceive and act in a manner similar to that of humans. We hope this chapter contributes to future development of human/computer interfaces, based on human haptics,

This research was supported by grants from the Japan Society for the Promotion of Science (JSPS), the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Tezukayama Educational Institution. Thanks to Professor R. G. Marteniuk, staff and

human/computer systems whose sensitivities are widely different.

perturbations to human vision, haptics, and goal-directed movement.

that can contribute to quality of human life and human experience.

will contribute to understanding how humans recognize an object as well as how humans dexterously manipulate an object or tool (MacKenzie & Iberall, 1994).

Another important issue for the future investigation is the connection between perceiving heaviness phase and the object lifting phase indicated in Fig. 1. How are heaviness perception and object manipulation interrelated? That is, what needs to be investigated is where heaviness ends and lifting begins (cf. Goodale, 1998) as well as whether or not humans make use of heaviness for object lifting in the sensorimotor system. The motor system for programming lifting forces is posited to operate independently of the perceptual system of heaviness (Goodale, 1998; Flanagan & Beltzner, 2000; Grandy & Westwood, 2006; Brayanov et al., 2010). This is based on the evidence that the load forces generated in the motor system quickly adapt to object weight while the heaviness perceptual system did not (Flanagan & Belzner, 2000; Grandy & Westwood, 2006; Flanagan et al., 2008). It seems, nevertheless, natural and reasonable to think that there should be some linkage enabling the exchange of some information, especially weight-related information, between the two systems (Maschke, et al., 2006), considering evidence related to the role of the sensorimotor system in heaviness perception (Sec. 2.1). It is believed that the solution of this actionperception matter will lead to the development of an optimal internal model in force programming to lift objects. These considerations, however, are not limited to heaviness, but probably hold true also for how human perceive movement and spatial orientation.

### **5.2 Computer graphics and haptic displays: Powerful tools to understand how humans perceive heaviness**

Computer graphic and haptic displays have recently become more popular and widely used as experimental tools - or environments - in research related to heaviness (Heineken & Schulte, 2007; Haggard & Jundi, 2009; Mawase & Karmiel, 2010). The reason for this may be that researchers have noticed practical advantages of using such devices for experimental control even if reality or physical presence is slightly sacrificed. The spatial resolutions and temporal lags for these devices are also important; with high resolution, the objects and environments created can affect the human sensorimotor and perceptual systems in the same manner as real, physical objects. However, such superior technologies should not be depended upon haphazardly since they exhibit, in some cases, difficulties in experimental replication. Therefore, whether or not to adopt and/or adapt evolving technology is dependent on research goals (Sec. 3.2). The experimental set-up should always be objectivecentered rather than technology-centered. Within this restriction, computer graphics and haptic displays have been incorporated into the experimental set-ups for this study. The resulting progress reveals the usefulness of such equipment and suggests many fundamental findings that can be expected from future experiments.

The perceived usefulness of these powerful tools includes:


will contribute to understanding how humans recognize an object as well as how humans

Another important issue for the future investigation is the connection between perceiving heaviness phase and the object lifting phase indicated in Fig. 1. How are heaviness perception and object manipulation interrelated? That is, what needs to be investigated is where heaviness ends and lifting begins (cf. Goodale, 1998) as well as whether or not humans make use of heaviness for object lifting in the sensorimotor system. The motor system for programming lifting forces is posited to operate independently of the perceptual system of heaviness (Goodale, 1998; Flanagan & Beltzner, 2000; Grandy & Westwood, 2006; Brayanov et al., 2010). This is based on the evidence that the load forces generated in the motor system quickly adapt to object weight while the heaviness perceptual system did not (Flanagan & Belzner, 2000; Grandy & Westwood, 2006; Flanagan et al., 2008). It seems, nevertheless, natural and reasonable to think that there should be some linkage enabling the exchange of some information, especially weight-related information, between the two systems (Maschke, et al., 2006), considering evidence related to the role of the sensorimotor system in heaviness perception (Sec. 2.1). It is believed that the solution of this actionperception matter will lead to the development of an optimal internal model in force programming to lift objects. These considerations, however, are not limited to heaviness, but

probably hold true also for how human perceive movement and spatial orientation.

**5.2 Computer graphics and haptic displays: Powerful tools to understand how** 

fundamental findings that can be expected from future experiments.

The perceived usefulness of these powerful tools includes:

similar manner as real, physical stimuli.

Computer graphic and haptic displays have recently become more popular and widely used as experimental tools - or environments - in research related to heaviness (Heineken & Schulte, 2007; Haggard & Jundi, 2009; Mawase & Karmiel, 2010). The reason for this may be that researchers have noticed practical advantages of using such devices for experimental control even if reality or physical presence is slightly sacrificed. The spatial resolutions and temporal lags for these devices are also important; with high resolution, the objects and environments created can affect the human sensorimotor and perceptual systems in the same manner as real, physical objects. However, such superior technologies should not be depended upon haphazardly since they exhibit, in some cases, difficulties in experimental replication. Therefore, whether or not to adopt and/or adapt evolving technology is dependent on research goals (Sec. 3.2). The experimental set-up should always be objectivecentered rather than technology-centered. Within this restriction, computer graphics and haptic displays have been incorporated into the experimental set-ups for this study. The resulting progress reveals the usefulness of such equipment and suggests many

1. The reality and presence of the environments and objects created by these computer displays depend on temporal and spatial precision, and on consistency of the timing, amplitude, and direction for forces/motions as humans interact with objects in the

2. The created stimuli can functionally act on human perceptual and motor systems in a

**humans perceive heaviness** 

environments.

dexterously manipulate an object or tool (MacKenzie & Iberall, 1994).


In the history of the development of haptic interfaces, little or no concern seems to have been paid to the human unit of heaviness. Instead, haptic devices - including robot hands and arms - have been developed based on the machine-centered unit of weight and reflected forces. This seems to hold true also for psychologists who have termed all psychological phenomena as illusions and have avoided interpreting them based on biological or physiological views. Of course, such weight-based devices have assisted humans to lift or manipulate a variety of objects in a smooth and safe manner. This success seems to depend, in large part, on efforts of users via their adaptation and/or learning systems, rather than via the engineered haptic systems. In the future, however, users of haptic devices will certainly include those lacking the abilities of adaptation and/or learning such as the elderly, the physically challenged, and medical patients who cannot easily adjust to such computer-centered systems. Thus, such systems developed in the future should be humancentered. Ideally such haptic devices should be suited for adaptation to the human haptic systems, to perceive and act in a manner similar to that of humans. We hope this chapter contributes to future development of human/computer interfaces, based on human haptics, that can contribute to quality of human life and human experience.
