The effects of contrast on visual orientation and spatial frequency discrimination: a comparison of single cells and behavior

“…range from proposals maintaining that the deployment of attention enhances the signal, to those stating that attention improves sensitivity by reducing external noise, to yet others that purport that the effects are due to observers’ decision criteria and/or reduction in spatial uncertainty.”

“…typically increases the response of a neuron to all orientations proportionately, so that a tuning curve constructed from responses to high-contrast stimuli is a multiplicatively scaled version of one made using lower contrast stimuli (Dean, 1981; Sclar and Freeman, 1982; Skottun et al., 1987).”

“Another way to describe this behavior is to say that the orientation tuning scaled with contrast, a property that has been repeatedly observed for both orientation tuning and spatial frequency tuning (Movshon et al., 1978c; Albrecht and Hamilton, 1982; Sclar and Freeman, 1982; Li and Creutzfeldt, 1984; Skottun et al.,…”

“trast independence of orientation tuning [22].”

“The observed values probably represent an upper bound on correlated firing, because adjacent neurons can safely be presumed to share common signals more than others (Braitenberg and Schiiz, 1991; Stevens, 1994; Douglas et al., 1995).”

“(a) The most prominent observation is of the contrast invariance of orientation selectivity (Sclar & Freeman 1982, Skottun et al 1987).”

“This is true in particular in the case of orientation, or direction of motion, for which contrast is known to have a purely multiplicative effect (Dean 1981, McAdams & Maunsell 1999, Sclar & Freeman 1982, Skottun et al. 1987).”

“We focused our research on the response to full-field sinusoidal gratings, because these are the only stimuli for which contrast dependence of orientation tuning has been studied (Sclar and Freeman, 1982; Skottun et al., 1987).”

“…in selecting out tualizing the effect of attention on single stimuli is illus-one of several stimuli from within the receptive field, trated in Figure 5C. Orientation tuning is largely invariantthe attentional signal that gives rise to this change in to changes in contrast (Skottun et al., 1987).”

“…tuning curves for orientation, as well as for other stimulus features, change very little in the face of large changes in stimulus contrast (Alitto and Usrey, 2004; Sclar and Freeman, 1982; Skottun et al., 1987), making these cells a model system for studying the mechanisms of tuning invariance.”

“…representations with contrast invariant tuning curves (Pouget et al., 2013), firing-rate tuning curves in the model also showed contrast invariance (Skottun et al., 1987); i.e., only their amplitude scaled with contrast, but their width remained roughly constant (Supplemental Experimental…”

“…connections puts followed by a fixed threshold would predict that the are found between geniculate relay cells and cortical orientation selectivity would decrease with increasing stimulus contrast in a way that is not observed experimentally (Sclar and Freeman, 1982; Skottun et al., 1987).”

“And yet, most simple cells respond with few or no spikes at the orthogonal orientation, and orientation tuning is largely contrast invariant (Alitto and Usrey, 2004; Anderson et al., 2000c; Ferster and Miller, 2000; Skottun et al., 1987).”

“…stimulus contrast typically makes a neuron's response stronger without changing its selectivity for orientation, direction, spatial frequency or stimulus position (Dean 1981; Holub & Morton-Gibson 1981; Sclar & Freeman 1982; Albrecht & Hamilton 1982; Skottun et al. 1987; Geisler & Albrecht 1997).”

“…basis for the observation that orientation tuning of visual cortical neurons is contrast invariant, i.e., changing stimulus contrast simply scales the magnitude of a neuron’s response, without changing the shape of its orientation tuning curve (Sclar and Freeman 1982; Skottun et al. 1987).”

“In V1, the width of orientation tuning of simple cells is invariant to stimulus contrast; the orientation tuning curve simply scales with contrast (Alitto and Usrey, 2004; Sclar and Freeman, 1982; Skottun et al., 1987).”

“Otherwise, the cell was classified as complex (Skottun et al., 1987).”

“…conducted in anesthetized and paralyzed animals have suggested that the ‘best cells’ in the striate cortex can signal differences in a visual parameter as small as can be discriminated behaviorally (Parker and Hawken, 1985; Swindale and Cynader, 1986; Bradley et al., 1987; Skottun et al., 1987).”

“…to assess the effect of attention on stimulus contrast because performance on this task improves with increasing contrast (Nachmias, 1967; Skottun et al., 1987; Lu and Dosher, 1998; Cameron et al., 2002), and because fMRI response increases monotonically with stimulus contrast (Boynton…”

“These firing rates are much lower than those reported elsewhere (Sclar and Freeman, 1982; Skottun et al., 1987; Anderson et al., 2000b).”

“Contrast invariance of orientation selectivity in the dLGN In V1, the response of orientation-selective cells increases with stimulus contrast, but their orientation selectivity is preserved, a phenomenon conventionally referred to as contrast invariance (Skottun et al., 1987).”

“…has been studied extensively in cat and monkey (Campbell et al., 1968; Schiller et al., 1976; Sclar and Freeman, 1982; Li and Creutzfeldt, 1984; Skottun et al., 1987; Douglas et al., 1991; Carandini and Ferster, 2000; Ringach et al., 2002; Volgushev et al., 2002; Monier et al., 2003; Nowak et…”

“Contrast response function and orientation tuning Our results confirm those of previous studies showing no relationship between stimulus contrast and bandwidth of orientation tuning (Anderson et al. 2000; Sclar and Freeman 1982; Skottun et al. 1987).”

“…real space is invariant with stimulus contrast (Song and Li 2008), and so too is the shape of the orientation tuning curve (Anderson et al. 2000b, Ferster and Miller 2000, Skottun et al. 1987) (contrast is monotonically related to the firing rate of the inputs to cortex (e.g. Ohzawa et al. 1985)).”

“…rates increase monotonically as a function of stimulus indentation in primary somatosensory cortex (Wang et al., 1995), as a function of whisker deflection velocity in barrel cortex (Wilent and Contreras, 2004), and as a function of stimulus contrast in primary visual cortex (Skottun et al., 1987).”

“For instance, data from both visual (Sclar and Freeman, 1982; Skottun et al., 1987) and somatosensory (Brumberg et al., 1996) cortex suggest that real cortical circuits maintain their sensitivities to preferred versus non-preferred stimuli over a wide range of signal-to-background ratios.”

“V1 simple cells maintain the shape and width of their tuning curves for orientation despite large changes that may occur in stimulus contrast (Sclar & Freeman 1982, Skottun et al. 1987, Alitto & Usrey 2004, Finn et al. 2007) (Figure 2a).”

“For example, a cortical neuron maintains its selectivity to a given stimulus parameter across a range of contrasts (Albrecht et al., 1984; Skottun et al., 1987), and its response to an optimal stimulus is inhibited by superimposing a nonoptimal stimulus (Morrone et al.”

“(A) Contrast invariance of orientation tuning curves recorded in cat V1 (data replotted from [46], Figure 3A).”

“However, contrast invariance of orientation selectivity (Skottun et al. 1987) cannot be accounted for by a purely excitatory feedforward model.”

“Yet, simple cells show contrastinvariant orientation tuning (Sclar and Freeman, 1982; Skottun et al., 1987; Anderson et al., 2000b), so that they respond to their preferred orientation even at very low contrast and often do not respond to the null orientation even at high contrast.”

“This has been observed for both spatial frequency tuning and orientation tuning (Skottun et al., 1987; Li and Creutzfeldt, 1984; Albrecht and Hamilton, 1982; Sclar and Freeman, 1982; Movshon et al., 1978a).”

“In particular, this family of models can explain response saturation (Albrecht and Hamilton, 1982), contrastinvariant tuning (Sclar and Freeman, 1982; Skottun et al., 1987; Albrecht and Geisler, 1991), and phase advance of response at high stimulus contrasts (Carandini et al., 1997).”

“Multiplicative interactions have also been observed between different stimulus dimensions (Tolhurst, 1973; Tolhurst and Movshon, 1975; Holub and Morton-Gibson, 1981; Albrecht and Hamilton, 1982; Sclar and Freeman, 1982; Skottun et al., 1987; Hamilton et al., 1989; Friend and Baker, 1993; McLean and Palmer, 1994; Geisl…”

“In the model, the outputs of LGN cells are threshold- linear, as in (6), due to the linear properties of LGN X cells, whereas the cortical outputs are represented by sigmoid signal functions (Sclar et al., 1985; Skottun et al., 1987; Maunsell et al., 1999), as in (5).”

“…found to be contrast invariant, as demonstrated by a constant tuning bandwidth in the face of increasing stimulus contrast (Movshon et al., 1978; Albrecht and Hamilton, 1982; Sclar and Freeman, 1982; Li and Creutzfeldt, 1984; Skottun et al., 1987; Alitto and Usrey, 2004; Niell and Stryker, 2008).”

“Such contrastinvariance has been quantitatively demonstrated for steady-state responses to drifting sinusoidal luminance gratings (Sclar and Freeman, 1982; Skottun et al., 1987; Anderson et al., 2000b).”

“This pattern of interactions helps in amplifying the external inputs and in achieving a relatively constant width for the orientation tuning curves, which is consistent with experimental findings on primary visual cortical neurons [43, 44].”

“Spatial frequency discrimination thresholds are not influenced by stimulus contrast (10–100%, Skottun et al., 1987) or inter-stimulus interval (ISI) duration in the short-term range (1–30 s, Magnussen, Greenlee, Asplund, & Dyrnes, 1990).”

“…of orientation tuning—a property shared by all simple cells thus far studied—almost certainly relies on intra-cortical sources of input to layer 4 neurons (Sclar and Freeman 1982; Skottun et al. 1987; Usrey and Alitto 2002; reviewed in Ferster and Miller 2000; Sompolinsky and Shapley 1997).”