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Nicole D. Anderson, Kathryn M. Murphy, David G. Jones; Temporal summation of dynamic orientation signals in noise. Journal of Vision 2004;4(8):493. doi: 10.1167/4.8.493.
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Using an orientation-in-noise stimulus, we have shown that orientation discrimination thresholds improve with increased size, but do not improve with increased duration of a static stimulus (Jones et al, 2003). Those results suggested oriented signals can be integrated over space but not time, however, simply increasing presentation time does not necessarily provide additional information. We investigated whether temporal summation contributes to orientation discrimination using a dynamic stimulus with multiple independent oriented samples presented over time. Two types of orientation-in-noise stimuli were used: a Global stimulus where the orientation signal extended across the display, and a Local stimulus where the orientation signal was spatially limited (Jones et al, 2003). Stimuli were high contrast and broadband in spatial frequency. In the dynamic condition, each frame was generated independently, so the stimuli were also broadband in temporal frequency. Thresholds were measured as the minimum amount of signal required to discriminate an oriented stimulus from unoriented noise in a 2IFC paradigm. Thresholds for static stimuli were the same for presentation times of 100ms and 1s. With dynamic stimuli, however, thresholds gradually improved from very brief (12ms) to remarkably long presentation times (>4s). Global thresholds improved from 51% to 20%, and Local thresholds improved from 26% to 7% orientation signal. Spatial integration of orientation signals is very efficient and can be understood in terms of a model based on signal detection theory, with performance limited by early and late stages of intrinsic noise. The nature of temporal summation is different, however, and is more consistent with probability summation of the outputs from low-level orientation detectors that operate over a very brief time scale, but whose outputs can be combined over a very long duration to yield better thresholds. Ref: Jones, Anderson, Murphy (2003) Vis Res 43:1223–1233
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