Patrick Langdon

Learning and maintaining saccadic accuracy: A model of brainstem--cerebellar interactions

Saccadic accuracy requires that the control signal sent to the motor neurons must be the right size to bring the fovea to the target, whatever the initial position of the eyes (and corresponding state of the eye muscles). Clinical and experimental evidence indicates that the basic machinery for generating saccadic eye movements, located in the brainstem, is not accurate: learning to make accurate saccades requires cerebellar circuitry located in the posterior vermis and fastigial nucleus. How do these two circuits interact to achieve adaptive control of saccades? A model of this interaction is described, based on Kawatos principle of feedback-error-learning. Its three components were (1) a simple controller with no knowledge of initial eye position, corresponding to the superior colliculus; (2) Robinsons internal feedback model of the saccadic burst generator, corresponding to preoculomotor areas in the brain-stem; and (3) Albuss Cerebellar Model Arithmetic Computer (CMK), a neural net model of the cerebellum. The connections between these components were (I) the simple feedback controller passed a (usually inaccurate) command to the pulse generator, and (2) a copy of this command to the CMAC; (3) the CMAC combined the copy with information about initial eye position to (4) alter the gain on the pulse generators internal feedback loop, thereby adjusting the size of burst sent to the motor neurons. (5) If the saccade were inaccurate, an error signal from the feedback controller adjusted the weights in the CMAC. It was proposed that connection (2) corresponds to the mossy fiber projection from superior colliculus to oculomotor vermis via the nucleus reticularis tegmenti pontis, and connection (5) to the climbing fiber projection from superior colliculus to the oculomotor vermis via the inferior olive. Plausible initialization values were chosen so that the system produced hypometric saccades (as do human infants) at the start of learning, and position-dependent hypermetric saccades when the cerebellum was removed. Simulations for horizontal eye movements showed that accurate saccades from any starting position could be learned rapidly, even if the error signal conveyed only whether the initial saccade were too large or too small. In subsequent tests the model adapted realistically both to simulated weakening of the eye muscles, and to intrasaccadic displacement of the target, thereby mimicking saccadic plasticity in adults. The architecture of the model may therefore offer a functional explanation of hitherto mysterious tectocerebellar projections, and a framework for investigating in greater detail how the cerebellum adaptively controls saccadic accuracy.

The effects of prior experience on the use of consumer products

Many products today are laden with a host of features which, for the majority of users, remain unused and often obscure the use of the simple features of use for which the product was devised (Norman in The design of everyday things. Basic Books, 2002; Keates and Clarkson in Countering design exclusion—an introduction to inclusive design. Springer, 2004). Since the cognitive capabilities of the marketed target group are largely not affected by age-related impairment, the intellectual demands of such products are frequently high (Rabbitt in Quart J Exp Psychol 46A(3):385–434, 1993). In addition, the age and technology generation of a product user will colour their expectations of the product interface and affect the range of skills they have available (Docampo in Technology generations handling complex User Interfaces. Ph. D. thesis, 2001). This paper addresses the issue of what features of products make them easy or difficult to learn to use, for the wider population as well as the older user, and whether and in what way individual prior experience affect the learning and use of a product design. To achieve the above, the interactions of users of varying ages and capabilities with two different everyday products were recorded in detail as they performed set tasks. Retrospective verbal protocols were then analysed using a category scheme based on an analysis of types of learning and cognition errors. This data was then compared with users’ performance on individual detailed experience questionnaires and a number of tests of general and specific cognitive capabilities. The principal finding was that similarity of prior experience to the usage situation was the main determinant of performance, although there was also some evidence for a gradual, age-related capability decline. Users of all ages adopted a means-end or trial and error interaction when faced with unfamiliar elements of the interaction. There was a strong technology generation effect such that older users were reluctant or unable to complete the required tasks for a digital camera.

Mouse movements of motion-impaired users: a submovement analysis

Understanding human movement is key to improving input devices and interaction techniques. This paper presents a study of mouse movements of motion-impaired users, with an aim to gaining a better understanding of impaired movement. The cursor trajectories of six motion-impaired users and three able-bodied users are studied according to their submovement structure. Several aspects of the movement are studied, including the frequency and duration of pauses between submovements, verification times, the number of submovements, the peak speed of submovements and the accuracy of submovements in two-dimensions. Results include findings that some motion-impaired users pause more often and for longer than able-bodied users, require up to five times more submovements to complete the same task, and exhibit a correlation between error and peak submovement speed that does not exist for able-bodied users.

Characterising user capabilities to support inclusive design evaluation

Designers require knowledge and data about users to effectively evaluate product accessibility during the early stages of design. This paper addresses this problem by setting out the sensory, cognitive and motor dimensions of user capability that are important for product interaction. The relationship between user capability and product demand is used as the underlying conceptual model for product design evaluations and for estimating the number of people potentially excluded from using a given product.

Designing Inclusive Interfaces Through User Modeling and Simulation

Elderly and disabled people can be hugely benefited through the advancement of modern electronic devices, as those can help them to engage more fully with the world. However, existing design practices often isolate elderly or disabled users by considering them as users with special needs. This article presents a simulator that can reflect problems faced by elderly and disabled users while they use computer, television, and similar electronic devices. The simulator embodies both the internal state of an application and the perceptual, cognitive, and motor processes of its user. It can help interface designers to understand, visualize, and measure the effect of impairment on interaction with an interface. Initially a brief survey of different user modeling techniques is presented, and then the existing models are classified into different categories. In the context of existing modeling approaches the work on user modeling is presented for people with a wide range of abilities. A few applications of the simulator, which shows the predictions are accurate enough to make design choices and point out the implication and limitations of the work, are also discussed.

Designing inclusive futures

Designing Inclusive Futures reflects the need to explore, in a coherent way, the issues and practicalities that lie behind design that is intended to extend our active future lives. This encompasses design for inclusion in daily life at home but also extends to the workplace and for products within these contexts. For example, given trends in employment sector growth, skills requirements, labour supply and demographic change, there is a need to predict the critical areas where individual capabilities are mismatched with the physical, social and organisational demands of work. This mismatch, which can be addressed within the domain of inclusive design, is pervasively linked to real artefacts in workspaces and their intersection with the health factors that relate to ageing. This book is the result of the fourth CWUAAT workshop held in Cambridge, England in April 2008. Contributions address the following themes: Understanding Users Inclusive Design Computer Access and New Technologies Assistive Technolo gy for Working and Daily Living Environments Inclusive Environments The nature of the contributions reflect a sample of the work of leading national and international researchers in the fields of Inclusive Design, Ergonomics, Universal Access, and Assistive and Rehabilitative Technology. There have been significant contributions from researchers in architecture, social housing provision, and apparel and fashion design, reflecting the need to understand the wider social and economic context of inclusive and assistive technology design.

Key influences on the user-centred design process

To develop inclusive design materials that are well suited to design practice and thus more likely to be adopted, a better understanding of this practice is needed. A triangulated study was thus conducted, including observations of case studies, interviews with designers and a literature review. The study examined many aspects of design practice, focusing on the consideration of users and influences on method uptake. Four overarching themes were identified: clients’ influence, informality, variation, and time and cost constraints. Implications include the need to educate clients in the value of inclusive design; the need for informal, cheap, yet insightful inclusive design methods; and the value of providing a range of flexible materials for different design situations.

Physical gestures for abstract concepts: Inclusive design with primary metaphors

Designers in inclusive design are challenged to create interactive products that cater for a wide range of prior experiences and cognitive abilities of their users. But suitable design guidance for this task is rare. This paper proposes the theory of primary metaphor and explores its validity as a source of design guidance. Primary metaphor theory describes how basic mental representations of physical sensorimotor experiences are extended to understand abstract domains. As primary metaphors are subconscious mental representations that are highly automated, they should be robustly available to people with differing levels of cognitive ability. Their proposed universality should make them accessible to people with differing levels of prior experience with technology. These predictions were tested for 12 primary metaphors that predict relations between spatial gestures and abstract interactive content. In an empirical study, 65 participants from two age groups (young and old) were asked to produce two-dimensional touch and three-dimensional free-form gestures in response to given abstract keywords and spatial dimensions of movements. The results show that across age groups in 92% of all cases users choose gestures that confirmed the predictions of the theory. Although the two age groups differed in their cognitive abilities and prior experience with technology, overall they did not differ in the amount of metaphor-congruent gestures they made. As predicted, only small or zero correlations of metaphor-congruent gestures with prior experience or cognitive ability could be found. The results provide a promising step toward inclusive design guidelines for gesture interaction with abstract content on mobile multitouch devices.

Designing accessible technology

This book was stimulated by the third Cambridge Workshop Series on Universal Access and Assistive Technology held in April 2006; the contributors represent leading researchers in the fields of Inclusive Design, Rehabilitation Robotics, Universal Access and Assistive Technology. Contributions focus on design issues for a more inclusive world; enabling computer access and the development of new technologies; assistive technology and rehabilitation robotics; and understanding users and involving them in design.

Universal access and assistive technology

This book contains the proceedings of the first Cambridge Workshop on Universal Access and Assistive Technology (CWUAAT), incorporating the fourth Cambridge Workshop on Rehabilitation Robotics, held in Cambridge, England in March 2002.