No abstract

No abstract

The desire to design systems right the first time and to produce designs thatare readily manufacturable is a goal passionately pursued byall engineers. Designers ofelectronic systems are no exception to this rule; the number and sophistication ofthe computer-aided design tools used daily bychip designers confirm this. Recently, however, designers oflarger electronic systems have also been turning to such tools ingrowing numbers. This article explores how a specific capability, simulation, has contributed to theirsuccess.

The purpose of this study was to optimise the testing paradigm for isolating the contributions of chromatic and achromatic mechanisms to the human spectral sensitivity function. Spectral sensitivity was determined for a test spot size of 1.2 deg presented with various spatial and temporal masks on a large, 10 deg background field of moderate intensity (1000 td) and colour temperature, CT = 2700 K. Sinusoidal temporal presentation (1 Hz) and a masking annulus of between 3 and 10 min of arc surrounding the test spot, was found to be most effective in separating chromatic from achromatic mechanisms. Square-wave (1 Hz) temporal presentation combined with the annulus was slightly less selective. The presence of the annulus did not affect the shape of flicker detection at 25 Hz which is a measure of the luminosity (achromatic) spectral sensitivity function.

The PERGs elicited by low contrast achromatic (luminance-modulated) and chromatic (isoluminant) gratings were studied as a function of the presentation mode (rapid onset, offset, reversal), departure from isoluminance, contrast and spatial frequency; predominantly phasic-type responses were found in all cases. We propose that the PERGs for low and moderate contrast, achromatic and chromatic grating stimuli, are generated by non-linear, transient retinal cells of the magno-system. Parvo retinal cells seem to contribute to the response only at higher chromatic contrasts. The transient nature of the PERG obtained from isoluminant gratings makes it doubtful that these signals represent the activity of colour-related processes.