桌球發球時宜之探討

Timing a serve in table tennis

知覺與動作息息相關相互影響，人類的行為很多都是經由知覺來產生動作，而桌球正手擊球這種截斷性動作（interceptive action），需要有絕佳的時宜才有最佳的運動表現。Lee（1976）曾以生態心理學的基礎，提出影像放大率與接觸時間的關係，認為由影像放大率的倒數（Tau值）可以作為用來估計接觸時間的知覺參數。目的：本研究便以檢驗Tau值作為啟動發球之知覺參數，探討不同技能水準者桌球發球的啟動訊息。方法：本研究共有14位實驗參加者，依桌球技術高低分為甲組（5位）、乙組（4位）、丙組（5位）。所有實驗參加者以三種不同高度的拋球方式進行切球發球，且球必須落在有效區域（25cmＸ25cm）才算成功，每人每種高度各發五球。結果：在三種拋球高度的情況下，僅有甲組動作時間不變，而以相對距離除以啟動時球的速度所得之Tau值，則在甲、丙組中均不受拋球高度的影響。結論：所觀察到的恆定Tau值支持生態心理學中有關訊息恆定性的主張，而甲組動作時間不受拋球高度影響的現象則歸因於高技能下執行動作進行微調的結果。

Many sport events require accurate perception of environmental information in order to provide the best performance. Interceptive movement such as many racket sports especially demand accurate timing skills for successful striking performance. From the perspective of ecological psychology, Lee (1976) and others have suggested that it is the rate of image expansion that specifies time to contact, and tmargin has been used as the perceptual parameter in approximating time to contact. Purpose: The purpose of the study was to investigate the trigger information (tmargin) and the skill levels for table tennis serve. MethodsAmong the 14 participants, 5 were members of the national team (group A), 4 were the college division B players (group B), and 5 were college students who had some table tennis experience but not members of varsity teams (group C). All the participants were tested under 3 different tossing heights for back spin serves. A 25cm2 area in the middle of the opposing table was used as the serving target, each participant had to have 5 serves into the target area for data analyses. Results: The results showed that only elite players maintained a constant movement time over different tossing heights for serves; tmargin, measured as the ratio of the ball height and the ball speed at the instance of the hand forward movement, however, was not significantly different over 3 tossing heights for all 3 levels of players. ConclusionThe concept of invariant is associated with the observed constant tmargin for all levels of players, and the constant movement time of the group A players is attributed to the fine tuning of the movement execution from the high level of skill.