Explanatory scope dual channel recod model
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Explanatory scope : Dual-channel RECOD model. Chapter 5, Pages 186-218. Harsha KASI PhD student, Institute of Microsystems and Microelectronics EPFL. Remember. Original sustained-transient model & RECOD model share common mechanisms critical to masking

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Explanatory scope dual channel recod model

Explanatory scope : Dual-channel RECOD model

Chapter 5, Pages 186-218

Harsha KASI

PhD student, Institute of Microsystems and Microelectronics

EPFL


Remember

Remember

  • Original sustained-transient model& RECOD model share common mechanisms critical to masking

  • Chapters 1, 2 and some additional results introduced in this chapter

  • Scope of 2 models by representative set of findings

Explanatory scope : Dual-channel RECOD model


Outline

Outline

  • Justification for effects and experimental findings – comparison of model simulations and psychophysical experiments

  • Explanatory power

  • Comparisons and critiques

Explanatory scope : Dual-channel RECOD model


Paracontrast and metacontrast suppression

Paracontrast and metacontrast suppression

Flicker persisted longer in the middle band

Flicker persisted longer in the double white arcs

Critical flicker frequency (CFF) : former ↑ latter

(target) (mask)

latter ↓ former

(mask) (target)

Paracontrast suppression

Metacontrast facilitation

→ Metacontrast suppression ?

Sherrington (1897)

Piéron (1935) – not only CFF but on brightness perception as well → metacontrast suppression

  • Metacontrast suppression (Brightness) – Faster transient activity by the lagging flash inhibiting the slower sustained response of the leading flash

  • Paracontrast suppression (CFF) – Slower sustained activity by the first stimulus reciprocally inhibiting the faster transient (flicker) by the second stimulus

  • 1st stimulus: higher CFF relative to the inhibited CFF of the 2nd stimulus

Explanatory scope : Dual-channel RECOD model


Transient masking effects

Transient masking effects

30-ms sinusoidal target grating at on-and offset of a 700-ms luminance flash mask (@ 54.8 cd/m2)

transient mask overshoots

Assume:

1.0 c/deg – low spatial frequency transient

7.8 c/deg – high spatial frequency sustained

Peripheral transient activity by mask flash adds ‘noise’ to the ‘signal’ of transient channels and not sustained channels

1.0 c/deg: SNR or Weber ratio in transient channel ↓→ overshoots!

7.8 c/deg: only a sustained masking effect at mask onset or offset

Green (1981)

Explanatory scope : Dual-channel RECOD model


Transient masking effects 2

Transient masking effects 2

Mitov et al. (1981): Overshoots inversely proportional to the spatial frequency of the grating – 2 c/deg6 c/deg18 c/deg

Spatial frequencies at and below 6-c/deg, and with spatial frequency increase if the magnitude of transient activation decreases and that of sustained channel increases

Teller et al., Matthews (1971): No overshoots with mask sizes e.g. <30’. However, with larger masks (e.g. > 60’)

Low spatial frequency gratings, optimal for activating transient channels under large conditioning flash mask

Breitmeyer and Julesz (1975) and Tulunay-Keesey and Bennis (1979): overshoots found in Green and Mittov’s studies depend on the rise and fall times of the mask at its on- and offsets

Slowly ramped instead of abrupt on- and offsets attenuate the transient response leading to curbing the transient masking overshoots

Matsumara’s (1976) work provides evidence to this !

Explanatory scope : Dual-channel RECOD model


Contour and surface dynamics unlumped p pathway

Contour and Surface dynamics – Unlumped p-pathway

Metacontrast: Strongest at shorter SOA for the contour compared to the surface/brightness network (20 ms vs. 60 ms)

Paracontrast:

Contour network – a long-lasting suppression coupled with a strong suppression – SOA ~ -10 ms

Surface network – Weaker long-lasting suppression and then enhancement

Identical set of equations with different weightings associated with inhibitory and facilitatory processes

Explanatory scope : Dual-channel RECOD model


M t ratio type b to a metacontrast

M/T Ratio – type B to A metacontrast

Transition : mask/target energy ratio is greater than unity

Difference in masking contrast thresholds

Type B @ lower mask contrasts and produced by a high-gain, rapid-saturation transient-on-sustained inhibition

transforms to a

Type A @ high mask contrasts, produced by a low-gain linear intra-channel sustained-on-sustained inhibition superimposed on the former inter-channel inhibition

Explanatory scope : Dual-channel RECOD model


Dichoptic type a forward and backward masking

Left

eye

Right

eye

Dichoptic type A forward and backward masking

Dichoptic type A forward masking by noise or structure is typically weaker than type A backward masking (Greenspoon and Eriksen 1968, Turvey 1973)

Forward masking by structure or noise:

Post-retinal transient activity can locally inhibit post-retinal sustained mask activity → less masking by integration

On the contrary, backward masking:

Sustained mask activity intrudes unobstructed into target’s sustained channels and @ post-retinal levels transient mask activity inhibits sustained target activity → facilitate intrusion – more masking !

Since these interactions are dichoptic, very likely exist at cortical levels

Explanatory scope : Dual-channel RECOD model


Explanatory scope dual channel recod model

Monoptic – Type A forward masking stronger than type A backward masking

Integration of target and mask activities occur early – photoreceptor and post-receptor neural levels prior to the centrally located sustained-transient inhibitory interactions

Type A forward and backward pattern masking as well as type B para- and metacontrast are obtained dichoptically and monoptically (Alpern 1953; Michaels and Turvey 1973, etc.)

Either integration in common sustained pathways or inter-channel inhibition

Type B metacontrast effects ↓ in magnitude as the spatial separation between the target and mask stimuli ↑ (Alpern 1953; Breitmeyer and Horman 1981, etc.)

Spatially restricted receptive fields of sustained and transient neurons & the topographical mapping between retina to the visual cortex (Brooks and Jung, 1973)

Explanatory scope : Dual-channel RECOD model


Reaction times contour interactions

Reaction times – contour interactions

In paracontrast, reaction times (∆RT) for target localisation increase

Paracontrast: Both data and model show an inverse U function

Metacontrast: constant function

Paracontrast: Both data and model show an inverse U function

Metacontrast: constant function

Change ∆RT in reaction times due to contour interactions between the target and mask as a function of SOA for two M/T contrast ratios. The middle curve corresponds to the average of the M/T=3 and M/T=1 data. Error bars represent ±1 SE of the mean. The squares are the predictions of the model. Reproduced from Ögmen et al. 2003

Paracontrast: close examination of M/T=3 and model – an inverse W function; peaks and dips shifted w.r.t each other

2 peaks in the W-shaped function – separate contributions of inter-channel sustained-on-transient inhibition and intra-channel transient-on-transient inhibition to reduce activity of the transient channels responding target

Explanatory scope : Dual-channel RECOD model


Explanatory scope dual channel recod model

Werner (1935): Metacontrast masking of a target pattern is inversely related to the orientation difference between target and mask stimuli

Cortical transient as well as sustained neurons are orientation selective (Ikeda and Wright 1975; Stone and Dreher 1973)

Mutual inhibition between cortical orientation-selective cells is itself orientation selective (Benvento et. al. 1972, etc.)

Blurred mask does not substantially reduce metacontrast of a non-blurred target

Transient channels are insensitive to high spatial frequencies and so to image blur (Growney, 1976)

Single-transient paradigm (Breitmeyer and Rudd 1981): Brief mask suppresses visibility of a prolonged sustained peripheral target for several seconds

Single-transient stimulus can activate transient-on-sustained inhibition, so despite the necessary 2-transient paradigm in metacontrast, contrary to Matin (1975).

Activation of T-M neurons is not required, transient neuron activation by mask alone is sufficient

Explanatory scope : Dual-channel RECOD model


Target recoverability

Target recoverability

Addition of a second mask (M2) to a target (T) and primary metacontrast mask (M1) can lead to the recovery of visibility of the target

  • Two effects:

  • M2-T-M1 :

  • Target visibility recovered

  • No change in the visibility of prim. mask M1

  • 2. T-M1-M2 :

  • No change in target visibility

  • A reduction in visibility of M1

Double disassociation, i.e., visibility and metacontrast masking effectiveness associated with sustained and transient responses

Target recovery: M2 inhibits M1’s transient activity sustained-on-transient inhibition

M1 reduced visibility : inter-channel transient-on-sustained inhibition by M2

Explanatory scope : Dual-channel RECOD model


Comparisons and critiques

Comparisons and Critiques

Apart from explaining various effects (Chap. 2), 2 models give adequate explanation of many variations of them as well

Revised version of Weisstein et al. 1975 accounts for metacontrast – transient-on-sustained inhibition of the non-recurrent forward type

For paracontrast: sustained-on-transient inhibition of the non-recurrent forward type

In conformance with assumption 1 of the Breitmeyer and Ganz’s model

Differs in assumptions 2 and 4, which in Breitmeyer’s models states that:

Paracontrast is realised via intra-channel inhibition effected in the sustained channels, rather than Weisstein’ et. al’s corresponding assumption of inter-channel, sustained-on-transition inhibition

Weisstein’s model cannot adequately account for the absence of type B metacontrast when simple reaction time or detection rather than brightness perception are used as criterion responses

Explanatory scope : Dual-channel RECOD model


Comparisons and critiques 2

Matin’s (1975) model with the sustained-transient model is not so similar in regard to required activation of T-M neurons

T-M neurons → transient; T neurons → sustained

Shorter response latency of T-M neurons compared with T neurons bears a similarity with the sustained-transient model

This combined with the inter-channel inhibition is equivalent to the assumptions 1 and 3 of the sustained-transient model and the fast-inhibition hypothesis of Weisstein’s

Comparisons and Critiques 2

RECOD model

Converges to sustained-transient model

Incorporating recent neurophysiological findings, feedback mechanisms, proposing additional feedforward, feedback-dominant phases of operation, explicit network structure and a quantitative description that can be simulated and compared directly with the experimental data

Explanatory scope : Dual-channel RECOD model


Comparisons and critiques 3

Comparisons and Critiques 3

Feedback structure aspect of RECOD model makes it comparable to some discussed in Chap. 4

Dual-channel aspect of RECOD model makes it significantly different from:

Bridgeman’s (1971, 1977, 1978) neural-network model

Ganz’s (1975) trace decay-lateral inhibition model

Reeves’s (1981) non-neural models

None of the neural or non-neural models incorporate the distinction between transient response components and slow sustained ones which can reciprocally inhibit each other

RECOD model incorporates:

Feedback (recurrent) connections as in Bridgeman’s single-channel model

Dual-channel structure to avoid spatiotemporal blurring that would occur in Bridgeman’s model so that perceptual dynamics can be organised as entities and can be processed individually

Explanatory scope : Dual-channel RECOD model


Summary

Summary

A review of psychophysical studies of spatiotemporal properties of human vision characterised by:

1. Separate pattern and movement or flicker thresholds

2. Temporal integration and persistence

3. Reaction time and effects of flicker adaptation

all as a function of spatial frequency→ existence of sustained/transient channels

Supported well by neurophysiological evidences – two parallel afferent pathways with similar characteristics

RECOD model adequately accounts for a wide range of visual masking phenomena discussed throughout this book !

Explanatory scope : Dual-channel RECOD model


Thank you for your attention

Thank you for your attention

Explanatory scope : Dual-channel RECOD model


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