The Effects of Active Lifting and Contact Force Distribution on Weight Discrimination

The Effects of Active Lifting and Contact Force Distribution on Weight Discrimination A thesis presented to the Psychology Department Graduate School of Arts and Sciences Brandeis University Waltham, Massachusetts By Benjamin A. Kramer The present experiment examined two questions pertaining to weight perception: 1) when objects are placed in a passively in the supported hands, does the distribution contact force from the object and from the supporting surface affect weight discrimination; and 2) does weight discrimination differ under conditions of passive support of the hand and active hefting? This study used ten subjects, and a standard adaptive staircase paradigm to measure the JND for weight discrimination. Each subject’s JND was measured in one active hefting condition and four conditions where weights were placed on their hands resting on a table. The four conditions involved different combinations of manipulations meant to widely distribute or focus the pressure of the object on the top of the hands or of the table on the bottom of the hands. All five active and passive conditions were repeated with a light weight (72g-84g) and heavy set (416g-510g), resulting in a total of ten conditions. JND’s were not affected by any of the different passive force distribution conditions. However, actively hefting the weights significantly reduced the JND relative to the passive conditions. Several hypotheses are discussed to explore the advantages of active hefting.