Ian Saunders PhD

Ian Saunders


Publications:
2012
  Continuous evolution of statistical estimators for optimal decision-making
Saunders, I & Vijayakumar, S 2012, 'Continuous evolution of statistical estimators for optimal decision-making' PLoS One, vol 7, no. 6, e37547. DOI: 10.1371/journal.pone.0037547
In many everyday situations, humans must make precise decisions in the presence of uncertain sensory information. For example, when asked to combine information from multiple sources we often assign greater weight to the more reliable information. It has been proposed that statistical-optimality often observed in human perception and decision-making requires that humans have access to the uncertainty of both their senses and their decisions. However, the mechanisms underlying the processes of uncertainty estimation remain largely unexplored. In this paper we introduce a novel visual tracking experiment that requires subjects to continuously report their evolving perception of the mean and uncertainty of noisy visual cues over time. We show that subjects accumulate sensory information over the course of a trial to form a continuous estimate of the mean, hindered only by natural kinematic constraints (sensorimotor latency etc.). Furthermore, subjects have access to a measure of their continuous objective uncertainty, rapidly acquired from sensory information available within a trial, but limited by natural kinematic constraints and a conservative margin for error. Our results provide the first direct evidence of the continuous mean and uncertainty estimation mechanisms in humans that may underlie optimal decision making.
General Information
Organisations: Institute of Perception, Action and Behaviour .
Authors: Saunders, Ian & Vijayakumar, Sethu.
Keywords: (, , . )
Number of pages: 14
Publication Date: 2012
Publication Information
Category: Article
Journal: PLoS One
Volume: 7
Issue number: 6
Original Language: English
DOIs: 10.1371/journal.pone.0037547
2011
  The role of feed-forward and feedback processes for closed-loop prosthesis control
Saunders, I & Vijayakumar, S 2011, 'The role of feed-forward and feedback processes for closed-loop prosthesis control' Journal of Neuroengineering and Rehabilitation, vol 8, no. October, 60. DOI: 10.1186/1743-0003-8-60
Background
It is widely believed that both feed-forward and feed-back mechanisms are required for successful object manipulation. Open-loop upper-limb prosthesis wearers receive no tactile feedback, which may be the cause of their limited dexterity and compromised grip force control. In this paper we ask whether observed prosthesis control impairments are due to lack of feedback or due to inadequate feed-forward control.

Methods
Healthy subjects were fitted with a closed-loop robotic hand and instructed to grasp and lift objects of different weights as we recorded trajectories and force profiles. We conducted three experiments under different feed-forward and feed-back configurations to elucidate the role of tactile feedback (i) in ideal conditions, (ii) under sensory deprivation, and (iii) under feed-forward uncertainty.

Results
(i) We found that subjects formed economical grasps in ideal conditions. (ii) To our surprise, this ability was preserved even when visual and tactile feedback were removed. (iii) When we introduced uncertainty into the hand controller performance degraded significantly in the absence of either visual or tactile feedback. Greatest performance was achieved when both sources of feedback were present.

Conclusions
We have introduced a novel method to understand the cognitive processes underlying grasping and lifting. We have shown quantitatively that tactile feedback can significantly improve performance in the presence of feed-forward uncertainty. However, our results indicate that feed-forward and feed-back mechanisms serve complementary roles, suggesting that to improve on the state-of-the-art in prosthetic hands we must develop prostheses that empower users to correct for the inevitable uncertainty in their feed-forward control.
General Information
Organisations: Institute of Perception, Action and Behaviour .
Authors: Saunders, Ian & Vijayakumar, Sethu.
Keywords: (, , . )
Number of pages: 12
Publication Date: 2011
Publication Information
Category: Article
Journal: Journal of Neuroengineering and Rehabilitation
Volume: 8
Issue number: October
Original Language: English
DOIs: 10.1186/1743-0003-8-60
  Continuous Estimation of Mean and Uncertainty
Saunders, I & Vijayakumar, S 2011, Continuous Estimation of Mean and Uncertainty. in 21st Annual Conference of the Japanese Neural Network Society. pp. P2-23.
Sensory uncertainty affects our perception and motor actions, but the mechanisms by which we estimate uncertainty are largely unexplored. We introduce a novel experimental paradigm that requires subjects to continuously report their (evolving) sufficient statistics of visual cues over time. We show that subjects rapidly accumulate evidence over the course of a trial to form an accurate estimate of the mean that equally weights all seen cues. Moreover, subjects have knowledge of their continuous objective uncertainty, although it is estimated with a conservative safety margin.
General Information
Organisations: Institute of Perception, Action and Behaviour .
Authors: Saunders, Ian & Vijayakumar, S..
Number of pages: 2
Pages: P2-23
Publication Date: 2011
Publication Information
Category: Conference contribution
Original Language: English
2010
  The role of hippocampal subregions in memory for stimulus associations
Langston, RF, Stevenson, CH, Wilson, CL, Saunders, I & Wood, ER 2010, 'The role of hippocampal subregions in memory for stimulus associations' Behavioural Brain Research, vol 215, no. 2, pp. 275-91. DOI: 10.1016/j.bbr.2010.07.006
The hippocampus is thought to be required for the associative recognition of objects together with the spatial or temporal contexts in which they occur. However, recent data showing that rats with fornix lesions perform as well as controls in an object-place task, while being impaired on an object-place-context task (Eacott & Norman, 2004), suggest that not all forms of context-dependent associative recognition depend on the integrity of the hippocampus. To examine the role of the hippocampus in context-dependent recognition directly, the present study tested the effects of large, selective, bilateral hippocampus lesions in rats on performance of a series of spontaneous recognition memory tasks: object recognition, object-place recognition, object-context recognition and object-place-context recognition. Consistent with the effects of fornix lesions, animals with hippocampus lesions were impaired only on the object-place-context task. These data confirm that not all forms of context-dependent associative recognition are mediated by the hippocampus. Subsequent experiments suggested that the object-place task does not require an allocentric representation of space, which could account for the lack of impairment following hippocampus lesions. Importantly, as the object-place-context task has similar spatial requirements, the selective deficit in object-place-context recognition suggests that this task requires hippocampus-dependent neural processes distinct from those required for allocentric spatial memory, or for object memory, object-place memory or object-context memory. Two possibilities are that object, place and context information converge only in the hippocampus, or that recognition of integrated object-place-context information requires a hippocampus-dependent mode of retrieval, such as recollection.
General Information
Organisations: Centre for Cognitive and Neural Systems.
Authors: Langston, R. F., Stevenson, C. H., Wilson, C. L., Saunders, Ian & Wood, E. R..
Keywords: (, , . )
Number of pages: 17
Pages: 275-91
Publication Date: Dec 2010
Publication Information
Category: Literature review
Journal: Behavioural Brain Research
Volume: 215
Issue number: 2
ISSN: 0166-4328
Original Language: English
DOIs: 10.1016/j.bbr.2010.07.006
2009
  A Closed Loop Prosthetic Hand as a Model Sensorimotor Circuit
Saunders, I & Vijayakumar, S 2009, 'A Closed Loop Prosthetic Hand as a Model Sensorimotor Circuit' Computiational Principles of Sensorimotor Learning (ESF International Workshop), Kloster Irsee, Germany, 13/09/09 - 15/09/09, .
We present a novel manipulandum for understanding the sensorimotor processes involved in object grasping. We have developed a closed-loop prosthetic hand, with 2 degrees of control and 32 channels of vibrotactile feedback of fingertip force and finger positions. In order to understand this model sensorimotor circuit we first tackle two sub-problems: (Q1) Do we integrate artificial sensory feedback (vibrotactile) with our other modalities (vision, proprioception) in a statistically optimal manner based on sensory uncertainty? We run subjects through a pursuit tracking task with noisy visual and vibrotactile cues to cursor location, and describe the resulting trajectories with a Kalman filter model; and (Q2) Are grasp trajectories and temporal force profiles a predictable function of the actuation commands that control the hand and the available feedback? We run subjects through a new tracking task where the grasp size and force on an object are modulated, and compare the resulting trajectories to those predicted by the optimal feedback control (OFC) framework.
General Information
Organisations: Institute of Perception, Action and Behaviour .
Authors: Saunders, Ian & Vijayakumar, Sethu.
Keywords: (Informatics, Computer Science. )
Number of pages: 2
Publication Date: 2009
Publication Information
Category: Poster
Original Language: English

Projects:
The role of tactile and proprioceptive feedback in the context of a closed-loop hand prosthesis. (PhD)