Integration of prior knowledge during haptic exploration depends on information type

Abstract

When haptically exploring softness, humans use higher peak forces when indenting harder versus softer objects. Here, we investigated the influence of different channels and types of prior knowledge on initial peak forces. Participants explored two stimuli (hard vs. soft) and judged which was softer. In Experiment 1 participants received either semantic (the words ''hard'' and ''soft''), visual (video of indentation), or prior information from recurring presentation (blocks of harder or softer pairs only). In a control condition no prior information was given (randomized presentation). In the recurring condition participants used higher initial forces when exploring harder stimuli. No effects were found in control and semantic conditions. With visual prior information, participants used less force for harder objects. We speculate that these findings reflect differences between implicit knowledge induced by recurring presentation and explicit knowledge induced by visual and semantic information. To test this hypothesis, we investigated whether explicit prior information interferes with implicit information in Experiment 2. Two groups of participants discriminated softness of harder or softer stimuli in two conditions (blocked and randomized). The interference group received additional explicit information during the blocked condition; the implicit-only group did not. Implicit prior information was only used for force adaptation when no additional explicit information was given, whereas explicit interfered with movement adaptation. The integration of prior knowledge only seems possible when implicit prior knowledge is induced-not with explicit knowledge.

Switching Between Objects Improves Precision in Haptic Perception of Softness

“…Overall our results suggest that in active touch perception where integration of information is limited by memory [16][17][18]20], the naturally applied strategy of switching between the stimuli [21] can be more beneficial for performance than prolonged accumulation of information about each stimulus.…”

“…In this case memory decay of the first object's representation should have had particularly pronounced negative effects on discrimination. However, in free explorations participants usually switch more often between the objects in order to compare them (in softness discrimination on average 4 times, given 6-14 indentations in total and an achieved performance of 85-90% correct [7,21]). This might be a strategy to cope with memory decay and improve discrimination performance.…”

Introduction to special issue on “Prediction in Perception and Action”

“…They monitor such learning by examining small anticipatory drifts and saccades in the direction of the most likely upcoming target. Zoeller et al (2019) show that such learning can be very specific. They show that somatosensory experience with hard or soft objects modifies the force observers use when interacting with the object.…”

Systematic Adaptation of Exploration Force to Exploration Duration in Softness Discrimination

“…However, perception relies on multiple information sources [6], and it is known that humans can use prior knowledge about object properties to adapt their exploratory behavior in haptic perception to the present task conditions [7,8]. For example, for softness perception results from our lab showed that humans use more force in the initial indentations when they expect to discriminate two harder objects as compared to two softer objects [2,4,9]. Humans also use higher forces when expecting less difference between the compliance of the to-be discriminated objects.…”

“…The compliance of an object is defined as the amount of an object's deformation under a given force [mm/N]. In previous studies investigating softness perception using a 2 Alternative Forced Choice (2AFC) discrimination task paradigm, participants were reported to perform 3 to 7 indentations per stimulus, when allowed to explore freely [2,4]. In free exploration, humans seem to stop exploring when they have sufficient information.…”