Research into Visual Perception conducted by Blackwell
In 1959 Blackwell published details of an eight-year programme of
research leading to the development of a general method by which optimum
illumination levels for various practical tasks were determined.
In this Blackwell describes a series of experiments
in which circular patches of light (stimuli) were presented to observers
for a range of durations,
the size and brightness of the stimuli also being varied systematically. On
each presentation interval, during which a stimulus may or may not
be shown, the observers
were asked to indicate if they perceived a stimulus. Subsequent experiments
of this type used rectangular and cross-shaped stimuli.
In 1960 Kincaid, Blackwell and Kristofferson presented a paper entitled
‘Neural Formulation of the Effects of Target Size and Shape upon
Visual Detection’, which they described as a ‘quantitative
general formulation for the effects of target size and shape upon visual
detection, in terms of a hypothesized neural mechanism of human vision’.
In this paper they stated that:
“ The foundations of the present hypothesis were laid by Graham,
Brown, and Mote in 1939. These authors suggested that the detectability
of a symmetrical target of uniform luminance is determined by the amount
of neural excitation produced at the centre of the neural representation
of the target, the amount of excitation being maximal at the centre
as a consequence of their assumption that every element of area within
target contributes excitation to the centre in proportion to a power
function of the distance of the element from the centre.”
However, Graham et.al. confined their discussion to circles and although
Kincaid et.al.’s title (Ref. 3., below) suggests that they
investigated the effects of target shape upon visual detection, the account
given is largely based on the results of experiments which employed only
circular targets. It is possible that the resulting formulation may also
apply to non-circular shapes, but no evidence was presented to indicate
that hypothesis had been tested.