Meeting of the Colour Group of Great Britain

Vision in the twilight zone: studies of visual performance under mesopic conditions

Thursday 11th November 2004

Rooms A & B, Northampton Suite, Refectory building level 4 (old level 6), City University

Organisers: Dr H C Walkey and Prof J L Barbur

The human visual system functions over a range of light intensity spanning approximately 10 log units. Operation over such a large range is possible largely through processes of adaptation. Much of this is due to the dual nature of the human retina; we have two types of photoreceptor, cones that operate at higher light levels and rods that operate at very low light levels. Mesopic vision describes the transition region from cone vision (photopic vision) to rod vision (scotopic vision), in which signals from both rods and cones contribute to the visual response. Many changes occur in this transition region that affect visual performance. Colour vision deteriorates as a result of reduced cone photoreceptor signals. The involvement of rod signals causes the spectral sensitivity of the eye to change, which has consequences for the measurement of luminance. At present there is no measure of luminance that reflects the spectral sensitivity of the eye in the mesopic range. Changes in pupil size alter the optics of the eye, resulting in changes in the quality of the retinal image. Differences in the operational characteristics of rods and cones lead to changes in spatial and temporal resolution as well as absolute sensitivity. Although the rod and cone systems are generally considered to operate independently, it is well known that many observed effects can only be explained in terms of rod-cone interactions. Work environments where the visual system has to perform, at least in part, under mesopic conditions are not uncommon. Some examples are: driving road vehicles/driving trains/flying aeroplanes at low light levels, security services/police surveillance work at low light levels, construction work at low light levels (some roadworks are now carried out at night). Little attention has been paid to understanding how visual performance changes under mesopic conditions. This one-day symposium aims to address the question of whether visual performance data can be used to describe mesopic light levels, and to explore the properties of vision at low light levels in order to gain a better understanding of the limits of visual performance in the mesopic range.

Abstracts for oral or poster presentations are welcome. The deadline for submitting abstracts was Monday 16th August 2004. Abstract submission details.

Registration will be required for non-presenters at this meeting. The deadline for registration was Friday 29th October 2004. Late registration is still possible. Registration form.

The meeting programme is now available.

Getting to the meeting:

• City University location
• Travel to London
• Travel to City University
• Local accomodation.

For further information contact:

City University Home | Applied Vision Research Centre | The Colour Group (GB)