Summation

About: Summation is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 45593 citations. The topic is also known as: summation & sum of a sequence.

A Behavioral Receptive Field for Ocular Following in Monkeys: Spatial Summation and Its Spatial Frequency Tuning

Abstract: In human and non-human primates, reflexive tracking eye movements can be initiated at very short latency in response to a rapid shift of the image. Previous studies in humans have shown that only a part of the central visual field is optimal for driving ocular following responses. Herein, we have investigated spatial summation of motion information across a wide range of spatial frequencies and speeds of drifting gratings by recording short-latency ocular following responses in macaque monkeys. We show that optimal stimulus size for driving ocular responses cover a small (<20° diameter), central part of the visual field that shrinks with higher spatial frequency. This signature of linear motion integration remains invariant with speed and temporal frequency. For low and medium spatial frequencies, we found a strong suppressive influence from surround motion, evidenced by a decrease of response amplitude for stimulus sizes larger than optimal. Such suppression disappears with gratings at high frequencies. The contribution of peripheral motion was investigated by presenting grating annuli of increasing eccentricity. We observed an exponential decay of response amplitude with grating eccentricity, the decrease being faster for higher spatial frequencies. Weaker surround suppression can thus be explained by sparser eccentric inputs at high frequencies. A Difference-of-Gaussians model best renders the antagonistic contributions of peripheral and central motions. Its best-fit parameters coincide with several, well-known spatial properties of area MT neuronal populations. These results describe the mechanism by which central motion information is automatically integrated in a context-dependent manner to drive ocular responses.Significance statementOcular following is driven by visual motion at ultra-short latency in both humans and monkeys. Its dynamics reflect the properties of low-level motion integration. Here, we show that a strong center-surround suppression mechanism modulates initial eye velocity. Its spatial properties are dependent upon visual inputs' spatial frequency but are insensitive to either its temporal frequency or speed. These properties are best described with a Difference-of-Gaussian model of spatial integration. The model parameters reflect many spatial characteristics of motion sensitive neuronal populations in monkey area MT. Our results further outline the computational properties of the behavioral receptive field underpinning automatic, context-dependent motion integration.

Temporal summation in age-related maculopathy

Abstract: We measured temporal summation in subjects with atrophic age-related maculopathy (ARM) and age-matched control subjects at photopic and scotopic luminance levels Although the ARM subjects did show longer critical durations in each case these differences were not statistically significant This result, in conjunction with our earlier work on temporal discrimination, indicates that the processes which are responsible for temporal summation of the eye (presumably located at the receptors) are more resistant to the degenerative processes of ARM than are those responsible for temporal discrimination This may be because the simple threshold procedure used here does not sufficiently stress the temporal response system to show a deficit

Duration effects of supraliminal electrical stimuli to the tongue.

Abstract: The investigation was concerned with temporal summation for supraliminal electrocutaneous stimuli to the tongue. One experiment (N = 5) dealt with pulse duration and a second experiment (N = 5) was...