HHF Part7 - Non-prehensive Skilled Movements

Part 7 Non-prehensive Skilled Movements

08/19/2024

이거 표하나로 요약되는 파트임.

"Gestures and Signs"

These three components of signs, namely, location, hand shape, and movement, are considered analogous to the phoneme in spoken language in that they occur below the level of the actual sign. In contrast to spoken languages, they occur simultaneously and not sequentially...

Uncommon or unfamiliar words are often spelled out by sign language interpreters using finger spelling. Studies of the hand movement sequences used when finger spelling indicate that the hand shape for a particular letter is influenced by the letters that precede and follow it. This has been interpreted as being analogous to the phenomenon of coarticulation in speech, in which certain phonemes are articulated differently depending on which phonemes follow (Jerde, Soechting, & Flanders, 2003).

"Pointing and Aiming Movements"

Pointing movements are made by the hand and arm toward a visually or proprioceptively defined target, but contact is not usually made with the target. Aiming movements do involve contact.

Pointing

As the amplitude of the movement increases, so too does the peak velocity, which means that movement time remains essentially constant (Georgopoulos, 1986).

The alternate hypothesis, the minimum jerk model, argues that movements are planned in extrinsic coordinates and that the desired path is straight but deviations occur due to inaccuracy in the controller, visual misperception of straight lines, and unavoidable errors (Flash & Hogan, 1985). The differences in the movement trajectories of blind-folded sighted and blind participants (Miall & Haggard, 1995) indicate that visual experience does affect the spatial path of the hand during pointing movements and that trajectory planning is not limited to simply minimizing some dynamic function.

They argue that the preferred coordinate system for controlling the kinematics of the arm is centered on the shoulder and not the head, because most of the errors in pointing were with respect to the distance that the arm had to be moved and not the direction of the movement (Flanders, Helms Tillery, & Soechting, 1992).

Aiming Movements

 

• Two Components of Aiming Movements: Woodworth (1899) identified two main components of goal-directed aiming movements: the initial ballistic movement and a subsequent deceleration phase controlled by visual feedback.
• Role of Visual Feedback: Visual feedback is crucial in enhancing movement accuracy, especially during the final phase of the movement trajectory. The time required for the visual feedback loop to operate is shorter than previously thought, ranging between 100-200 ms.
• Fitts' Law: Fitts (1954) proposed a law predicting movement time based on the trade-off between speed and accuracy. Movement time is dependent on the amplitude of the movement and the width of the target, encapsulated in the "index of difficulty."
• Application of Fitts' Law: Fitts' law applies broadly to hand and arm movements, including precise manipulative tasks, but has limitations in predicting movement times in very short movements and bimanual tasks with different target widths.
• Movement Time and Visual Feedback: Increased movement time with higher indices of difficulty occurs primarily in the terminal phase of the movement, where feedback control becomes essential. Visual feedback, particularly in the final phase, allows for trajectory adjustments and reduced aiming errors.

 

The core idea is that as the distance to the target increases, or as the target size decreases, the time required to hit the target also increases. This relationship is known as the speed-accuracy trade-off.

However, it does not predict accurately the movement times in short movements (Klapp, 1975), nor in bimanual tasks in which the hands move to targets of very different widths (i.e., discrepant indices of difficulty). Under these conditions, the arm movements are synchronized so that the hands arrive at the targets simultaneously, as shown in figure 7.5 (Kelso, Southard, & Goodman, 1979).

 

"Keyboard Skills" 

Takeaways

• Comparison of Typing and Piano Playing: Both involve finger movements to depress keys but differ in rhythm and force requirements. Typing focuses on speed and accuracy in key sequences, while piano playing involves rhythmic timing and controlled force for sound dynamics.
• Typing Skills: Typing requires specific training and involves multiple cognitive and motor processes, including chunking text, translating it into finger movements, and executing keystrokes. Skilled typists can process and anticipate several characters ahead, improving speed and accuracy.
• Piano Playing Skills: Piano playing involves not just technical execution but also musical interpretation, such as controlling tempo and dynamics. Skilled pianists can sight-read and anticipate musical notes, similar to how typists anticipate keystrokes.
• Eye-Hand Span: Both typists and pianists develop an ability to process and plan movements several steps ahead of their current position. This anticipatory skill distinguishes experts from novices.
• Parallel Processing in Typing: Skilled typists often overlap finger movements, allowing them to type more quickly and fluidly compared to novices who type each key sequentially.
• Expert Performance: Whether in typing, piano playing, or telegraphy, expert performers demonstrate an ability to remember and execute longer sequences of actions, facilitated by their ability to look or listen ahead and prepare their responses.

> What is sight-read here "Skilled pianists can sight-read and anticipate musical notes, similar to how typists anticipate keystrokes."?

"Sight-read" refers to the ability of skilled pianists to play a piece of music they have never seen before, directly from the written musical notation, without prior practice or familiarity with the piece.

> I don't understand "Parallel Processing in Typing". Elaborate with an example.

Skilled Typist (Parallel Processing):

• Step 1: The skilled typist reads the entire word "cat" in one glance and starts planning the finger movements for each letter.
• Step 2: As their finger presses the "c" key, they are already moving another finger towards the "a" key and preparing for the "t" key.
• Step 3: By the time "c" is pressed, the "a" key is almost ready to be pressed, and the process flows smoothly into the "t" key without pause.

 

Takeaways Continued 

• Types of Typing Errors: Typing errors can be categorized into four main types—substitutions, intrusions, omissions, and transpositions—each with distinct characteristics and causes. For example, substitution errors often involve incorrect finger assignment, while omission errors are linked to insufficient key press force.
• Role of Kinesthetic and Tactile Feedback: Typists rely on kinesthetic feedback (sensing movement) to detect and correct errors. Tactile feedback (feeling the key press) is crucial for movement accuracy and error detection but not for maintaining typing rhythm.

> What do you mean by typing rhythm here?

When I say that tactile feedback is not crucial for maintaining typing rhythm, I mean that even if a typist can't feel the keys as they press them (e.g., due to anesthetization or typing above the keyboard), they can often still maintain the regular timing or rhythm of their keystrokes. 

 

Takeaways Continued 

 

• Keystroke Timing: Skilled typists generally have keystroke intervals of 100-200 ms, with faster intervals when using opposite hands. The QWERTY layout is suboptimal, but alternatives don't necessarily improve speed.
• Motoric vs Cognitive Constraints: Skilled typists are primarily limited by motoric constraints, whereas novices are constrained by cognitive factors. Typing speed is relatively unaffected by the semantic content of the text.
• Piano vs Typing: Both expert typists and pianists operate near the mechanical and neural limits of the human hand, with similar peak movement speeds.
• Force Dynamics: In typing, the force applied to keys is loosely controlled and generally consistent across fingers. In piano playing, force is actively controlled for musical expression.
• Finger Tapping: Tapping speed can reveal neurological and motor skill differences, with right-handed typists often showing faster tapping rates with the left hand after extensive training. There are also gender differences in tapping rates, potentially due to hand size.

 

"Bimanual Music Skills" 

Bimanual music skills, such as playing stringed, wind, or percussion instruments, involve complex motor tasks that require extensive and explicit training to develop expertise. These skills are associated with significant cortical plasticity, particularly in the sensory and motor cortices. Expert musicians, especially string players, exhibit enlarged cortical representations of the digits used in playing, highlighting the brain's adaptation to repetitive, specialized tasks. Once acquired, these skills are resilient but require regular practice to maintain. The ability to plan movements ahead, seen in both expert musicians and typists, is a key factor that differentiates experts from novices.